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# sql/elements.py
# Copyright (C) 2005-2020 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php
"""Core SQL expression elements, including :class:`_expression.ClauseElement`,
:class:`_expression.ColumnElement`, and derived classes.
"""
from __future__ import unicode_literals
import itertools
import numbers
import operator
import re
from . import operators
from . import type_api
from .annotation import Annotated
from .base import _generative
from .base import Executable
from .base import Immutable
from .base import NO_ARG
from .base import PARSE_AUTOCOMMIT
from .visitors import cloned_traverse
from .visitors import traverse
from .visitors import Visitable
from .. import exc
from .. import inspection
from .. import util
def _clone(element, **kw):
return element._clone()
def _document_text_coercion(paramname, meth_rst, param_rst):
return util.add_parameter_text(
paramname,
(
".. warning:: "
"The %s argument to %s can be passed as a Python string argument, "
"which will be treated "
"as **trusted SQL text** and rendered as given. **DO NOT PASS "
"UNTRUSTED INPUT TO THIS PARAMETER**."
)
% (param_rst, meth_rst),
)
def collate(expression, collation):
"""Return the clause ``expression COLLATE collation``.
e.g.::
collate(mycolumn, 'utf8_bin')
produces::
mycolumn COLLATE utf8_bin
The collation expression is also quoted if it is a case sensitive
identifier, e.g. contains uppercase characters.
.. versionchanged:: 1.2 quoting is automatically applied to COLLATE
expressions if they are case sensitive.
"""
expr = _literal_as_binds(expression)
return BinaryExpression(
expr, CollationClause(collation), operators.collate, type_=expr.type
)
def between(expr, lower_bound, upper_bound, symmetric=False):
"""Produce a ``BETWEEN`` predicate clause.
E.g.::
from sqlalchemy import between
stmt = select([users_table]).where(between(users_table.c.id, 5, 7))
Would produce SQL resembling::
SELECT id, name FROM user WHERE id BETWEEN :id_1 AND :id_2
The :func:`.between` function is a standalone version of the
:meth:`_expression.ColumnElement.between` method available on all
SQL expressions, as in::
stmt = select([users_table]).where(users_table.c.id.between(5, 7))
All arguments passed to :func:`.between`, including the left side
column expression, are coerced from Python scalar values if a
the value is not a :class:`_expression.ColumnElement` subclass.
For example,
three fixed values can be compared as in::
print(between(5, 3, 7))
Which would produce::
:param_1 BETWEEN :param_2 AND :param_3
:param expr: a column expression, typically a
:class:`_expression.ColumnElement`
instance or alternatively a Python scalar expression to be coerced
into a column expression, serving as the left side of the ``BETWEEN``
expression.
:param lower_bound: a column or Python scalar expression serving as the
lower bound of the right side of the ``BETWEEN`` expression.
:param upper_bound: a column or Python scalar expression serving as the
upper bound of the right side of the ``BETWEEN`` expression.
:param symmetric: if True, will render " BETWEEN SYMMETRIC ". Note
that not all databases support this syntax.
.. versionadded:: 0.9.5
.. seealso::
:meth:`_expression.ColumnElement.between`
"""
expr = _literal_as_binds(expr)
return expr.between(lower_bound, upper_bound, symmetric=symmetric)
def literal(value, type_=None):
r"""Return a literal clause, bound to a bind parameter.
Literal clauses are created automatically when non-
:class:`_expression.ClauseElement` objects (such as strings, ints, dates,
etc.) are
used in a comparison operation with a :class:`_expression.ColumnElement`
subclass,
such as a :class:`~sqlalchemy.schema.Column` object. Use this function
to force the generation of a literal clause, which will be created as a
:class:`BindParameter` with a bound value.
:param value: the value to be bound. Can be any Python object supported by
the underlying DB-API, or is translatable via the given type argument.
:param type\_: an optional :class:`~sqlalchemy.types.TypeEngine` which
will provide bind-parameter translation for this literal.
"""
return BindParameter(None, value, type_=type_, unique=True)
def outparam(key, type_=None):
"""Create an 'OUT' parameter for usage in functions (stored procedures),
for databases which support them.
The ``outparam`` can be used like a regular function parameter.
The "output" value will be available from the
:class:`~sqlalchemy.engine.ResultProxy` object via its ``out_parameters``
attribute, which returns a dictionary containing the values.
"""
return BindParameter(key, None, type_=type_, unique=False, isoutparam=True)
def not_(clause):
"""Return a negation of the given clause, i.e. ``NOT(clause)``.
The ``~`` operator is also overloaded on all
:class:`_expression.ColumnElement` subclasses to produce the
same result.
"""
return operators.inv(_literal_as_binds(clause))
@inspection._self_inspects
class ClauseElement(Visitable):
"""Base class for elements of a programmatically constructed SQL
expression.
"""
__visit_name__ = "clause"
_annotations = {}
supports_execution = False
_from_objects = []
bind = None
_is_clone_of = None
is_selectable = False
is_clause_element = True
description = None
_order_by_label_element = None
_is_from_container = False
def _clone(self):
"""Create a shallow copy of this ClauseElement.
This method may be used by a generative API. Its also used as
part of the "deep" copy afforded by a traversal that combines
the _copy_internals() method.
"""
c = self.__class__.__new__(self.__class__)
c.__dict__ = self.__dict__.copy()
ClauseElement._cloned_set._reset(c)
ColumnElement.comparator._reset(c)
# this is a marker that helps to "equate" clauses to each other
# when a Select returns its list of FROM clauses. the cloning
# process leaves around a lot of remnants of the previous clause
# typically in the form of column expressions still attached to the
# old table.
c._is_clone_of = self
return c
@property
def _constructor(self):
"""return the 'constructor' for this ClauseElement.
This is for the purposes for creating a new object of
this type. Usually, its just the element's __class__.
However, the "Annotated" version of the object overrides
to return the class of its proxied element.
"""
return self.__class__
@util.memoized_property
def _cloned_set(self):
"""Return the set consisting all cloned ancestors of this
ClauseElement.
Includes this ClauseElement. This accessor tends to be used for
FromClause objects to identify 'equivalent' FROM clauses, regardless
of transformative operations.
"""
s = util.column_set()
f = self
# note this creates a cycle, asserted in test_memusage. however,
# turning this into a plain @property adds tends of thousands of method
# calls to Core / ORM performance tests, so the small overhead
# introduced by the relatively small amount of short term cycles
# produced here is preferable
while f is not None:
s.add(f)
f = f._is_clone_of
return s
def __getstate__(self):
d = self.__dict__.copy()
d.pop("_is_clone_of", None)
return d
def _annotate(self, values):
"""return a copy of this ClauseElement with annotations
updated by the given dictionary.
"""
return Annotated(self, values)
def _with_annotations(self, values):
"""return a copy of this ClauseElement with annotations
replaced by the given dictionary.
"""
return Annotated(self, values)
def _deannotate(self, values=None, clone=False):
"""return a copy of this :class:`_expression.ClauseElement`
with annotations
removed.
:param values: optional tuple of individual values
to remove.
"""
if clone:
# clone is used when we are also copying
# the expression for a deep deannotation
return self._clone()
else:
# if no clone, since we have no annotations we return
# self
return self
def _execute_on_connection(self, connection, multiparams, params):
if self.supports_execution:
return connection._execute_clauseelement(self, multiparams, params)
else:
raise exc.ObjectNotExecutableError(self)
def unique_params(self, *optionaldict, **kwargs):
"""Return a copy with :func:`bindparam()` elements replaced.
Same functionality as ``params()``, except adds `unique=True`
to affected bind parameters so that multiple statements can be
used.
"""
return self._params(True, optionaldict, kwargs)
def params(self, *optionaldict, **kwargs):
"""Return a copy with :func:`bindparam()` elements replaced.
Returns a copy of this ClauseElement with :func:`bindparam()`
elements replaced with values taken from the given dictionary::
>>> clause = column('x') + bindparam('foo')
>>> print(clause.compile().params)
{'foo':None}
>>> print(clause.params({'foo':7}).compile().params)
{'foo':7}
"""
return self._params(False, optionaldict, kwargs)
def _params(self, unique, optionaldict, kwargs):
if len(optionaldict) == 1:
kwargs.update(optionaldict[0])
elif len(optionaldict) > 1:
raise exc.ArgumentError(
"params() takes zero or one positional dictionary argument"
)
def visit_bindparam(bind):
if bind.key in kwargs:
bind.value = kwargs[bind.key]
bind.required = False
if unique:
bind._convert_to_unique()
return cloned_traverse(self, {}, {"bindparam": visit_bindparam})
def compare(self, other, **kw):
r"""Compare this ClauseElement to the given ClauseElement.
Subclasses should override the default behavior, which is a
straight identity comparison.
\**kw are arguments consumed by subclass compare() methods and
may be used to modify the criteria for comparison.
(see :class:`_expression.ColumnElement`)
"""
return self is other
def _copy_internals(self, clone=_clone, **kw):
"""Reassign internal elements to be clones of themselves.
Called during a copy-and-traverse operation on newly
shallow-copied elements to create a deep copy.
The given clone function should be used, which may be applying
additional transformations to the element (i.e. replacement
traversal, cloned traversal, annotations).
"""
pass
def get_children(self, **kwargs):
r"""Return immediate child elements of this
:class:`_expression.ClauseElement`.
This is used for visit traversal.
\**kwargs may contain flags that change the collection that is
returned, for example to return a subset of items in order to
cut down on larger traversals, or to return child items from a
different context (such as schema-level collections instead of
clause-level).
"""
return []
def self_group(self, against=None):
"""Apply a 'grouping' to this :class:`_expression.ClauseElement`.
This method is overridden by subclasses to return a
"grouping" construct, i.e. parenthesis. In particular
it's used by "binary" expressions to provide a grouping
around themselves when placed into a larger expression,
as well as by :func:`_expression.select` constructs when placed into
the FROM clause of another :func:`_expression.select`. (Note that
subqueries should be normally created using the
:meth:`_expression.Select.alias` method, as many platforms require
nested SELECT statements to be named).
As expressions are composed together, the application of
:meth:`self_group` is automatic - end-user code should never
need to use this method directly. Note that SQLAlchemy's
clause constructs take operator precedence into account -
so parenthesis might not be needed, for example, in
an expression like ``x OR (y AND z)`` - AND takes precedence
over OR.
The base :meth:`self_group` method of
:class:`_expression.ClauseElement`
just returns self.
"""
return self
@util.dependencies("sqlalchemy.engine.default")
def compile(self, default, bind=None, dialect=None, **kw):
"""Compile this SQL expression.
The return value is a :class:`~.Compiled` object.
Calling ``str()`` or ``unicode()`` on the returned value will yield a
string representation of the result. The
:class:`~.Compiled` object also can return a
dictionary of bind parameter names and values
using the ``params`` accessor.
:param bind: An ``Engine`` or ``Connection`` from which a
``Compiled`` will be acquired. This argument takes precedence over
this :class:`_expression.ClauseElement`'s bound engine, if any.
:param column_keys: Used for INSERT and UPDATE statements, a list of
column names which should be present in the VALUES clause of the
compiled statement. If ``None``, all columns from the target table
object are rendered.
:param dialect: A ``Dialect`` instance from which a ``Compiled``
will be acquired. This argument takes precedence over the `bind`
argument as well as this :class:`_expression.ClauseElement`
's bound engine,
if any.
:param inline: Used for INSERT statements, for a dialect which does
not support inline retrieval of newly generated primary key
columns, will force the expression used to create the new primary
key value to be rendered inline within the INSERT statement's
VALUES clause. This typically refers to Sequence execution but may
also refer to any server-side default generation function
associated with a primary key `Column`.
:param compile_kwargs: optional dictionary of additional parameters
that will be passed through to the compiler within all "visit"
methods. This allows any custom flag to be passed through to
a custom compilation construct, for example. It is also used
for the case of passing the ``literal_binds`` flag through::
from sqlalchemy.sql import table, column, select
t = table('t', column('x'))
s = select([t]).where(t.c.x == 5)
print(s.compile(compile_kwargs={"literal_binds": True}))
.. versionadded:: 0.9.0
.. seealso::
:ref:`faq_sql_expression_string`
"""
if not dialect:
if bind:
dialect = bind.dialect
elif self.bind:
dialect = self.bind.dialect
bind = self.bind
else:
dialect = default.StrCompileDialect()
return self._compiler(dialect, bind=bind, **kw)
def _compiler(self, dialect, **kw):
"""Return a compiler appropriate for this ClauseElement, given a
Dialect."""
return dialect.statement_compiler(dialect, self, **kw)
def __str__(self):
if util.py3k:
return str(self.compile())
else:
return unicode(self.compile()).encode( # noqa
"ascii", "backslashreplace"
) # noqa
@util.deprecated(
"0.9",
"The :meth:`_expression.ClauseElement.__and__` "
"method is deprecated and will "
"be removed in a future release. Conjunctions should only be "
"used from a :class:`_expression.ColumnElement` subclass, e.g. "
":meth:`_expression.ColumnElement.__and__`.",
)
def __and__(self, other):
"""'and' at the ClauseElement level.
"""
return and_(self, other)
@util.deprecated(
"0.9",
"The :meth:`_expression.ClauseElement.__or__` "
"method is deprecated and will "
"be removed in a future release. Conjunctions should only be "
"used from a :class:`_expression.ColumnElement` subclass, e.g. "
":meth:`_expression.ColumnElement.__or__`.",
)
def __or__(self, other):
"""'or' at the ClauseElement level.
"""
return or_(self, other)
def __invert__(self):
if hasattr(self, "negation_clause"):
return self.negation_clause
else:
return self._negate()
def _negate(self):
return UnaryExpression(
self.self_group(against=operators.inv),
operator=operators.inv,
negate=None,
)
def __bool__(self):
raise TypeError("Boolean value of this clause is not defined")
__nonzero__ = __bool__
def __repr__(self):
friendly = self.description
if friendly is None:
return object.__repr__(self)
else:
return "<%s.%s at 0x%x; %s>" % (
self.__module__,
self.__class__.__name__,
id(self),
friendly,
)
class ColumnElement(operators.ColumnOperators, ClauseElement):
"""Represent a column-oriented SQL expression suitable for usage in the
"columns" clause, WHERE clause etc. of a statement.
While the most familiar kind of :class:`_expression.ColumnElement` is the
:class:`_schema.Column` object, :class:`_expression.ColumnElement`
serves as the basis
for any unit that may be present in a SQL expression, including
the expressions themselves, SQL functions, bound parameters,
literal expressions, keywords such as ``NULL``, etc.
:class:`_expression.ColumnElement`
is the ultimate base class for all such elements.
A wide variety of SQLAlchemy Core functions work at the SQL expression
level, and are intended to accept instances of
:class:`_expression.ColumnElement` as
arguments. These functions will typically document that they accept a
"SQL expression" as an argument. What this means in terms of SQLAlchemy
usually refers to an input which is either already in the form of a
:class:`_expression.ColumnElement` object,
or a value which can be **coerced** into
one. The coercion rules followed by most, but not all, SQLAlchemy Core
functions with regards to SQL expressions are as follows:
* a literal Python value, such as a string, integer or floating
point value, boolean, datetime, ``Decimal`` object, or virtually
any other Python object, will be coerced into a "literal bound
value". This generally means that a :func:`.bindparam` will be
produced featuring the given value embedded into the construct; the
resulting :class:`.BindParameter` object is an instance of
:class:`_expression.ColumnElement`.
The Python value will ultimately be sent
to the DBAPI at execution time as a parameterized argument to the
``execute()`` or ``executemany()`` methods, after SQLAlchemy
type-specific converters (e.g. those provided by any associated
:class:`.TypeEngine` objects) are applied to the value.
* any special object value, typically ORM-level constructs, which
feature a method called ``__clause_element__()``. The Core
expression system looks for this method when an object of otherwise
unknown type is passed to a function that is looking to coerce the
argument into a :class:`_expression.ColumnElement` expression. The
``__clause_element__()`` method, if present, should return a
:class:`_expression.ColumnElement` instance. The primary use of
``__clause_element__()`` within SQLAlchemy is that of class-bound
attributes on ORM-mapped classes; a ``User`` class which contains a
mapped attribute named ``.name`` will have a method
``User.name.__clause_element__()`` which when invoked returns the
:class:`_schema.Column`
called ``name`` associated with the mapped table.
* The Python ``None`` value is typically interpreted as ``NULL``,
which in SQLAlchemy Core produces an instance of :func:`.null`.
A :class:`_expression.ColumnElement` provides the ability to generate new
:class:`_expression.ColumnElement`
objects using Python expressions. This means that Python operators
such as ``==``, ``!=`` and ``<`` are overloaded to mimic SQL operations,
and allow the instantiation of further :class:`_expression.ColumnElement`
instances
which are composed from other, more fundamental
:class:`_expression.ColumnElement`
objects. For example, two :class:`.ColumnClause` objects can be added
together with the addition operator ``+`` to produce
a :class:`.BinaryExpression`.
Both :class:`.ColumnClause` and :class:`.BinaryExpression` are subclasses
of :class:`_expression.ColumnElement`::
>>> from sqlalchemy.sql import column
>>> column('a') + column('b')
<sqlalchemy.sql.expression.BinaryExpression object at 0x101029dd0>
>>> print(column('a') + column('b'))
a + b
.. seealso::
:class:`_schema.Column`
:func:`_expression.column`
"""
__visit_name__ = "column_element"
primary_key = False
foreign_keys = []
_proxies = ()
_label = None
"""The named label that can be used to target
this column in a result set.
This label is almost always the label used when
rendering <expr> AS <label> in a SELECT statement. It also
refers to a name that this column expression can be located from
in a result set.
For a regular Column bound to a Table, this is typically the label
<tablename>_<columnname>. For other constructs, different rules
may apply, such as anonymized labels and others.
"""
key = None
"""the 'key' that in some circumstances refers to this object in a
Python namespace.
This typically refers to the "key" of the column as present in the
``.c`` collection of a selectable, e.g. sometable.c["somekey"] would
return a Column with a .key of "somekey".
"""
_key_label = None
"""A label-based version of 'key' that in some circumstances refers
to this object in a Python namespace.
_key_label comes into play when a select() statement is constructed with
apply_labels(); in this case, all Column objects in the ``.c`` collection
are rendered as <tablename>_<columnname> in SQL; this is essentially the
value of ._label. But to locate those columns in the ``.c`` collection,
the name is along the lines of <tablename>_<key>; that's the typical
value of .key_label.
"""
_render_label_in_columns_clause = True
"""A flag used by select._columns_plus_names that helps to determine
we are actually going to render in terms of "SELECT <col> AS <label>".
This flag can be returned as False for some Column objects that want
to be rendered as simple "SELECT <col>"; typically columns that don't have
any parent table and are named the same as what the label would be
in any case.
"""
_resolve_label = None
"""The name that should be used to identify this ColumnElement in a
select() object when "label resolution" logic is used; this refers
to using a string name in an expression like order_by() or group_by()
that wishes to target a labeled expression in the columns clause.
The name is distinct from that of .name or ._label to account for the case
where anonymizing logic may be used to change the name that's actually
rendered at compile time; this attribute should hold onto the original
name that was user-assigned when producing a .label() construct.
"""
_allow_label_resolve = True
"""A flag that can be flipped to prevent a column from being resolvable
by string label name."""
_is_implicitly_boolean = False
_alt_names = ()
def self_group(self, against=None):
if (
against in (operators.and_, operators.or_, operators._asbool)
and self.type._type_affinity is type_api.BOOLEANTYPE._type_affinity
):
return AsBoolean(self, operators.istrue, operators.isfalse)
elif against in (operators.any_op, operators.all_op):
return Grouping(self)
else:
return self
def _negate(self):
if self.type._type_affinity is type_api.BOOLEANTYPE._type_affinity:
return AsBoolean(self, operators.isfalse, operators.istrue)
else:
return super(ColumnElement, self)._negate()
@util.memoized_property
def type(self):
return type_api.NULLTYPE
@util.memoized_property
def comparator(self):
try:
comparator_factory = self.type.comparator_factory
except AttributeError as err:
util.raise_(
TypeError(
"Object %r associated with '.type' attribute "
"is not a TypeEngine class or object" % self.type
),
replace_context=err,
)
else:
return comparator_factory(self)
def __getattr__(self, key):
try:
return getattr(self.comparator, key)
except AttributeError as err:
util.raise_(
AttributeError(
"Neither %r object nor %r object has an attribute %r"
% (
type(self).__name__,
type(self.comparator).__name__,
key,
)
),
replace_context=err,
)
def operate(self, op, *other, **kwargs):
return op(self.comparator, *other, **kwargs)
def reverse_operate(self, op, other, **kwargs):
return op(other, self.comparator, **kwargs)
def _bind_param(self, operator, obj, type_=None):
return BindParameter(
None,
obj,
_compared_to_operator=operator,
type_=type_,
_compared_to_type=self.type,
unique=True,
)
@property
def expression(self):
"""Return a column expression.
Part of the inspection interface; returns self.
"""
return self
@property
def _select_iterable(self):
return (self,)
@util.memoized_property
def base_columns(self):
return util.column_set(c for c in self.proxy_set if not c._proxies)
@util.memoized_property
def proxy_set(self):
s = util.column_set([self])
for c in self._proxies:
s.update(c.proxy_set)
return s
def _uncached_proxy_set(self):
"""An 'uncached' version of proxy set.
This is so that we can read annotations from the list of columns
without breaking the caching of the above proxy_set.
"""
s = util.column_set([self])
for c in self._proxies:
s.update(c._uncached_proxy_set())
return s
def shares_lineage(self, othercolumn):
"""Return True if the given :class:`_expression.ColumnElement`
has a common ancestor to this :class:`_expression.ColumnElement`."""
return bool(self.proxy_set.intersection(othercolumn.proxy_set))
def _compare_name_for_result(self, other):
"""Return True if the given column element compares to this one
when targeting within a result row."""
return (
hasattr(other, "name")
and hasattr(self, "name")
and other.name == self.name
)
def _make_proxy(
self, selectable, name=None, name_is_truncatable=False, **kw
):
"""Create a new :class:`_expression.ColumnElement` representing this
:class:`_expression.ColumnElement`
as it appears in the select list of a
descending selectable.
"""
if name is None:
name = self.anon_label
if self.key:
key = self.key
else:
try:
key = str(self)
except exc.UnsupportedCompilationError:
key = self.anon_label
else:
key = name
co = ColumnClause(
_as_truncated(name) if name_is_truncatable else name,
type_=getattr(self, "type", None),
_selectable=selectable,
)
co._proxies = [self]
if selectable._is_clone_of is not None:
co._is_clone_of = selectable._is_clone_of.columns.get(key)
selectable._columns[key] = co
return co
def compare(self, other, use_proxies=False, equivalents=None, **kw):
"""Compare this ColumnElement to another.
Special arguments understood:
:param use_proxies: when True, consider two columns that
share a common base column as equivalent (i.e. shares_lineage())
:param equivalents: a dictionary of columns as keys mapped to sets
of columns. If the given "other" column is present in this
dictionary, if any of the columns in the corresponding set() pass
the comparison test, the result is True. This is used to expand the
comparison to other columns that may be known to be equivalent to
this one via foreign key or other criterion.
"""
to_compare = (other,)
if equivalents and other in equivalents:
to_compare = equivalents[other].union(to_compare)
for oth in to_compare:
if use_proxies and self.shares_lineage(oth):
return True
elif hash(oth) == hash(self):
return True
else:
return False
def cast(self, type_):
"""Produce a type cast, i.e. ``CAST(<expression> AS <type>)``.
This is a shortcut to the :func:`_expression.cast` function.
.. seealso::
:ref:`coretutorial_casts`
:func:`_expression.cast`
:func:`_expression.type_coerce`
.. versionadded:: 1.0.7
"""
return Cast(self, type_)
def label(self, name):
"""Produce a column label, i.e. ``<columnname> AS <name>``.
This is a shortcut to the :func:`_expression.label` function.
if 'name' is None, an anonymous label name will be generated.
"""
return Label(name, self, self.type)
@util.memoized_property
def anon_label(self):
"""provides a constant 'anonymous label' for this ColumnElement.
This is a label() expression which will be named at compile time.
The same label() is returned each time anon_label is called so
that expressions can reference anon_label multiple times, producing
the same label name at compile time.
the compiler uses this function automatically at compile time
for expressions that are known to be 'unnamed' like binary
expressions and function calls.
"""
while self._is_clone_of is not None:
self = self._is_clone_of
return _anonymous_label(
"%%(%d %s)s" % (id(self), getattr(self, "name", "anon"))
)
class BindParameter(ColumnElement):
r"""Represent a "bound expression".
:class:`.BindParameter` is invoked explicitly using the
:func:`.bindparam` function, as in::
from sqlalchemy import bindparam
stmt = select([users_table]).\
where(users_table.c.name == bindparam('username'))
Detailed discussion of how :class:`.BindParameter` is used is
at :func:`.bindparam`.
.. seealso::
:func:`.bindparam`
"""
__visit_name__ = "bindparam"
_is_crud = False
_expanding_in_types = ()
def __init__(
self,
key,
value=NO_ARG,
type_=None,
unique=False,
required=NO_ARG,
quote=None,
callable_=None,
expanding=False,
isoutparam=False,
_compared_to_operator=None,
_compared_to_type=None,
):
r"""Produce a "bound expression".
The return value is an instance of :class:`.BindParameter`; this
is a :class:`_expression.ColumnElement`
subclass which represents a so-called
"placeholder" value in a SQL expression, the value of which is
supplied at the point at which the statement in executed against a
database connection.
In SQLAlchemy, the :func:`.bindparam` construct has
the ability to carry along the actual value that will be ultimately
used at expression time. In this way, it serves not just as
a "placeholder" for eventual population, but also as a means of
representing so-called "unsafe" values which should not be rendered
directly in a SQL statement, but rather should be passed along
to the :term:`DBAPI` as values which need to be correctly escaped
and potentially handled for type-safety.
When using :func:`.bindparam` explicitly, the use case is typically
one of traditional deferment of parameters; the :func:`.bindparam`
construct accepts a name which can then be referred to at execution
time::
from sqlalchemy import bindparam
stmt = select([users_table]).\
where(users_table.c.name == bindparam('username'))
The above statement, when rendered, will produce SQL similar to::
SELECT id, name FROM user WHERE name = :username
In order to populate the value of ``:username`` above, the value
would typically be applied at execution time to a method
like :meth:`_engine.Connection.execute`::
result = connection.execute(stmt, username='wendy')
Explicit use of :func:`.bindparam` is also common when producing
UPDATE or DELETE statements that are to be invoked multiple times,
where the WHERE criterion of the statement is to change on each
invocation, such as::
stmt = (users_table.update().
where(user_table.c.name == bindparam('username')).
values(fullname=bindparam('fullname'))
)
connection.execute(
stmt, [{"username": "wendy", "fullname": "Wendy Smith"},
{"username": "jack", "fullname": "Jack Jones"},
]
)
SQLAlchemy's Core expression system makes wide use of
:func:`.bindparam` in an implicit sense. It is typical that Python
literal values passed to virtually all SQL expression functions are
coerced into fixed :func:`.bindparam` constructs. For example, given
a comparison operation such as::
expr = users_table.c.name == 'Wendy'
The above expression will produce a :class:`.BinaryExpression`
construct, where the left side is the :class:`_schema.Column` object
representing the ``name`` column, and the right side is a
:class:`.BindParameter` representing the literal value::
print(repr(expr.right))
BindParameter('%(4327771088 name)s', 'Wendy', type_=String())
The expression above will render SQL such as::
user.name = :name_1
Where the ``:name_1`` parameter name is an anonymous name. The
actual string ``Wendy`` is not in the rendered string, but is carried
along where it is later used within statement execution. If we
invoke a statement like the following::
stmt = select([users_table]).where(users_table.c.name == 'Wendy')
result = connection.execute(stmt)
We would see SQL logging output as::
SELECT "user".id, "user".name
FROM "user"
WHERE "user".name = %(name_1)s
{'name_1': 'Wendy'}
Above, we see that ``Wendy`` is passed as a parameter to the database,
while the placeholder ``:name_1`` is rendered in the appropriate form
for the target database, in this case the PostgreSQL database.
Similarly, :func:`.bindparam` is invoked automatically
when working with :term:`CRUD` statements as far as the "VALUES"
portion is concerned. The :func:`_expression.insert`
construct produces an
``INSERT`` expression which will, at statement execution time,
generate bound placeholders based on the arguments passed, as in::
stmt = users_table.insert()
result = connection.execute(stmt, name='Wendy')
The above will produce SQL output as::
INSERT INTO "user" (name) VALUES (%(name)s)
{'name': 'Wendy'}
The :class:`_expression.Insert` construct,
at compilation/execution time,
rendered a single :func:`.bindparam` mirroring the column
name ``name`` as a result of the single ``name`` parameter
we passed to the :meth:`_engine.Connection.execute` method.
:param key:
the key (e.g. the name) for this bind param.
Will be used in the generated
SQL statement for dialects that use named parameters. This
value may be modified when part of a compilation operation,
if other :class:`BindParameter` objects exist with the same
key, or if its length is too long and truncation is
required.
:param value:
Initial value for this bind param. Will be used at statement
execution time as the value for this parameter passed to the
DBAPI, if no other value is indicated to the statement execution
method for this particular parameter name. Defaults to ``None``.
:param callable\_:
A callable function that takes the place of "value". The function
will be called at statement execution time to determine the
ultimate value. Used for scenarios where the actual bind
value cannot be determined at the point at which the clause
construct is created, but embedded bind values are still desirable.
:param type\_:
A :class:`.TypeEngine` class or instance representing an optional
datatype for this :func:`.bindparam`. If not passed, a type
may be determined automatically for the bind, based on the given
value; for example, trivial Python types such as ``str``,
``int``, ``bool``
may result in the :class:`.String`, :class:`.Integer` or
:class:`.Boolean` types being automatically selected.
The type of a :func:`.bindparam` is significant especially in that
the type will apply pre-processing to the value before it is
passed to the database. For example, a :func:`.bindparam` which
refers to a datetime value, and is specified as holding the
:class:`.DateTime` type, may apply conversion needed to the
value (such as stringification on SQLite) before passing the value
to the database.
:param unique:
if True, the key name of this :class:`.BindParameter` will be
modified if another :class:`.BindParameter` of the same name
already has been located within the containing
expression. This flag is used generally by the internals
when producing so-called "anonymous" bound expressions, it
isn't generally applicable to explicitly-named :func:`.bindparam`
constructs.
:param required:
If ``True``, a value is required at execution time. If not passed,
it defaults to ``True`` if neither :paramref:`.bindparam.value`
or :paramref:`.bindparam.callable` were passed. If either of these
parameters are present, then :paramref:`.bindparam.required`
defaults to ``False``.
:param quote:
True if this parameter name requires quoting and is not
currently known as a SQLAlchemy reserved word; this currently
only applies to the Oracle backend, where bound names must
sometimes be quoted.
:param isoutparam:
if True, the parameter should be treated like a stored procedure
"OUT" parameter. This applies to backends such as Oracle which
support OUT parameters.
:param expanding:
if True, this parameter will be treated as an "expanding" parameter
at execution time; the parameter value is expected to be a sequence,
rather than a scalar value, and the string SQL statement will
be transformed on a per-execution basis to accommodate the sequence
with a variable number of parameter slots passed to the DBAPI.
This is to allow statement caching to be used in conjunction with
an IN clause.
.. seealso::
:meth:`.ColumnOperators.in_`
:ref:`baked_in` - with baked queries
.. note:: The "expanding" feature does not support "executemany"-
style parameter sets.
.. versionadded:: 1.2
.. versionchanged:: 1.3 the "expanding" bound parameter feature now
supports empty lists.
.. seealso::
:ref:`coretutorial_bind_param`
:ref:`coretutorial_insert_expressions`
:func:`.outparam`
"""
if isinstance(key, ColumnClause):
type_ = key.type
key = key.key
if required is NO_ARG:
required = value is NO_ARG and callable_ is None
if value is NO_ARG:
value = None
if quote is not None:
key = quoted_name(key, quote)
if unique:
self.key = _anonymous_label(
"%%(%d %s)s"
% (
id(self),
re.sub(r"[%\(\) \$]+", "_", key).strip("_")
if key is not None
else "param",
)
)
else:
self.key = key or _anonymous_label("%%(%d param)s" % id(self))
# identifying key that won't change across
# clones, used to identify the bind's logical
# identity
self._identifying_key = self.key
# key that was passed in the first place, used to
# generate new keys
self._orig_key = key or "param"
self.unique = unique
self.value = value
self.callable = callable_
self.isoutparam = isoutparam
self.required = required
self.expanding = expanding
if type_ is None:
if _compared_to_type is not None:
self.type = _compared_to_type.coerce_compared_value(
_compared_to_operator, value
)
else:
self.type = type_api._resolve_value_to_type(value)
elif isinstance(type_, type):
self.type = type_()
else:
self.type = type_
def _with_expanding_in_types(self, types):
"""Return a copy of this :class:`.BindParameter` in
the context of an expanding IN against a tuple.
"""
cloned = self._clone()
cloned._expanding_in_types = types
return cloned
def _with_value(self, value):
"""Return a copy of this :class:`.BindParameter` with the given value
set.
"""
cloned = self._clone()
cloned.value = value
cloned.callable = None
cloned.required = False
if cloned.type is type_api.NULLTYPE:
cloned.type = type_api._resolve_value_to_type(value)
return cloned
@property
def effective_value(self):
"""Return the value of this bound parameter,
taking into account if the ``callable`` parameter
was set.
The ``callable`` value will be evaluated
and returned if present, else ``value``.
"""
if self.callable:
return self.callable()
else:
return self.value
def _clone(self):
c = ClauseElement._clone(self)
if self.unique:
c.key = _anonymous_label(
"%%(%d %s)s" % (id(c), c._orig_key or "param")
)
return c
def _convert_to_unique(self):
if not self.unique:
self.unique = True
self.key = _anonymous_label(
"%%(%d %s)s" % (id(self), self._orig_key or "param")
)
def compare(self, other, **kw):
"""Compare this :class:`BindParameter` to the given
clause."""
return (
isinstance(other, BindParameter)
and self.type._compare_type_affinity(other.type)
and self.value == other.value
and self.callable == other.callable
)
def __getstate__(self):
"""execute a deferred value for serialization purposes."""
d = self.__dict__.copy()
v = self.value
if self.callable:
v = self.callable()
d["callable"] = None
d["value"] = v
return d
def __setstate__(self, state):
if state.get("unique", False):
state["key"] = _anonymous_label(
"%%(%d %s)s" % (id(self), state.get("_orig_key", "param"))
)
self.__dict__.update(state)
def __repr__(self):
return "BindParameter(%r, %r, type_=%r)" % (
self.key,
self.value,
self.type,
)
class TypeClause(ClauseElement):
"""Handle a type keyword in a SQL statement.
Used by the ``Case`` statement.
"""
__visit_name__ = "typeclause"
def __init__(self, type_):
self.type = type_
class TextClause(Executable, ClauseElement):
"""Represent a literal SQL text fragment.
E.g.::
from sqlalchemy import text
t = text("SELECT * FROM users")
result = connection.execute(t)
The :class:`_expression.TextClause` construct is produced using the
:func:`_expression.text`
function; see that function for full documentation.
.. seealso::
:func:`_expression.text`
"""
__visit_name__ = "textclause"
_bind_params_regex = re.compile(r"(?<![:\w\x5c]):(\w+)(?!:)", re.UNICODE)
_execution_options = Executable._execution_options.union(
{"autocommit": PARSE_AUTOCOMMIT}
)
_is_implicitly_boolean = False
def __and__(self, other):
# support use in select.where(), query.filter()
return and_(self, other)
@property
def _select_iterable(self):
return (self,)
@property
def selectable(self):
# allows text() to be considered by
# _interpret_as_from
return self
_hide_froms = []
# help in those cases where text() is
# interpreted in a column expression situation
key = _label = _resolve_label = None
_allow_label_resolve = False
def __init__(self, text, bind=None):
self._bind = bind
self._bindparams = {}
def repl(m):
self._bindparams[m.group(1)] = BindParameter(m.group(1))
return ":%s" % m.group(1)
# scan the string and search for bind parameter names, add them
# to the list of bindparams
self.text = self._bind_params_regex.sub(repl, text)
@classmethod
@util.deprecated_params(
autocommit=(
"0.6",
"The :paramref:`_expression.text.autocommit` "
"parameter is deprecated and "
"will be removed in a future release. Please use the "
":paramref:`.Connection.execution_options.autocommit` parameter "
"in conjunction with the :meth:`.Executable.execution_options` "
"method.",
),
bindparams=(
"0.9",
"The :paramref:`_expression.text.bindparams` parameter "
"is deprecated and will be removed in a future release. Please "
"refer to the :meth:`_expression.TextClause.bindparams` method.",
),
typemap=(
"0.9",
"The :paramref:`_expression.text.typemap` parameter is "
"deprecated and will be removed in a future release. Please "
"refer to the :meth:`_expression.TextClause.columns` method.",
),
)
@_document_text_coercion("text", ":func:`.text`", ":paramref:`.text.text`")
def _create_text(
self, text, bind=None, bindparams=None, typemap=None, autocommit=None
):
r"""Construct a new :class:`_expression.TextClause` clause,
representing
a textual SQL string directly.
E.g.::
from sqlalchemy import text
t = text("SELECT * FROM users")
result = connection.execute(t)
The advantages :func:`_expression.text`
provides over a plain string are
backend-neutral support for bind parameters, per-statement
execution options, as well as
bind parameter and result-column typing behavior, allowing
SQLAlchemy type constructs to play a role when executing
a statement that is specified literally. The construct can also
be provided with a ``.c`` collection of column elements, allowing
it to be embedded in other SQL expression constructs as a subquery.
Bind parameters are specified by name, using the format ``:name``.
E.g.::
t = text("SELECT * FROM users WHERE id=:user_id")
result = connection.execute(t, user_id=12)
For SQL statements where a colon is required verbatim, as within
an inline string, use a backslash to escape::
t = text("SELECT * FROM users WHERE name='\:username'")
The :class:`_expression.TextClause`
construct includes methods which can
provide information about the bound parameters as well as the column
values which would be returned from the textual statement, assuming
it's an executable SELECT type of statement. The
:meth:`_expression.TextClause.bindparams`
method is used to provide bound
parameter detail, and :meth:`_expression.TextClause.columns`
method allows
specification of return columns including names and types::
t = text("SELECT * FROM users WHERE id=:user_id").\
bindparams(user_id=7).\
columns(id=Integer, name=String)
for id, name in connection.execute(t):
print(id, name)
The :func:`_expression.text` construct is used in cases when
a literal string SQL fragment is specified as part of a larger query,
such as for the WHERE clause of a SELECT statement::
s = select([users.c.id, users.c.name]).where(text("id=:user_id"))
result = connection.execute(s, user_id=12)
:func:`_expression.text` is also used for the construction
of a full, standalone statement using plain text.
As such, SQLAlchemy refers
to it as an :class:`.Executable` object, and it supports
the :meth:`Executable.execution_options` method. For example,
a :func:`_expression.text`
construct that should be subject to "autocommit"
can be set explicitly so using the
:paramref:`.Connection.execution_options.autocommit` option::
t = text("EXEC my_procedural_thing()").\
execution_options(autocommit=True)
Note that SQLAlchemy's usual "autocommit" behavior applies to
:func:`_expression.text` constructs implicitly - that is,
statements which begin
with a phrase such as ``INSERT``, ``UPDATE``, ``DELETE``,
or a variety of other phrases specific to certain backends, will
be eligible for autocommit if no transaction is in progress.
:param text:
the text of the SQL statement to be created. use ``:<param>``
to specify bind parameters; they will be compiled to their
engine-specific format.
:param autocommit: whether or not to set the "autocommit" execution
option for this :class:`_expression.TextClause` object.
:param bind:
an optional connection or engine to be used for this text query.
:param bindparams:
A list of :func:`.bindparam` instances used to
provide information about parameters embedded in the statement.
E.g.::
stmt = text("SELECT * FROM table WHERE id=:id",
bindparams=[bindparam('id', value=5, type_=Integer)])
:param typemap:
A dictionary mapping the names of columns represented in the columns
clause of a ``SELECT`` statement to type objects.
E.g.::
stmt = text("SELECT * FROM table",
typemap={'id': Integer, 'name': String},
)
.. seealso::
:ref:`sqlexpression_text` - in the Core tutorial
:ref:`orm_tutorial_literal_sql` - in the ORM tutorial
"""
stmt = TextClause(text, bind=bind)
if bindparams:
stmt = stmt.bindparams(*bindparams)
if typemap:
stmt = stmt.columns(**typemap)
if autocommit is not None:
stmt = stmt.execution_options(autocommit=autocommit)
return stmt
@_generative
def bindparams(self, *binds, **names_to_values):
"""Establish the values and/or types of bound parameters within
this :class:`_expression.TextClause` construct.
Given a text construct such as::
from sqlalchemy import text
stmt = text("SELECT id, name FROM user WHERE name=:name "
"AND timestamp=:timestamp")
the :meth:`_expression.TextClause.bindparams`
method can be used to establish
the initial value of ``:name`` and ``:timestamp``,
using simple keyword arguments::
stmt = stmt.bindparams(name='jack',
timestamp=datetime.datetime(2012, 10, 8, 15, 12, 5))
Where above, new :class:`.BindParameter` objects
will be generated with the names ``name`` and ``timestamp``, and
values of ``jack`` and ``datetime.datetime(2012, 10, 8, 15, 12, 5)``,
respectively. The types will be
inferred from the values given, in this case :class:`.String` and
:class:`.DateTime`.
When specific typing behavior is needed, the positional ``*binds``
argument can be used in which to specify :func:`.bindparam` constructs
directly. These constructs must include at least the ``key``
argument, then an optional value and type::
from sqlalchemy import bindparam
stmt = stmt.bindparams(
bindparam('name', value='jack', type_=String),
bindparam('timestamp', type_=DateTime)
)
Above, we specified the type of :class:`.DateTime` for the
``timestamp`` bind, and the type of :class:`.String` for the ``name``
bind. In the case of ``name`` we also set the default value of
``"jack"``.
Additional bound parameters can be supplied at statement execution
time, e.g.::
result = connection.execute(stmt,
timestamp=datetime.datetime(2012, 10, 8, 15, 12, 5))
The :meth:`_expression.TextClause.bindparams`
method can be called repeatedly,
where it will re-use existing :class:`.BindParameter` objects to add
new information. For example, we can call
:meth:`_expression.TextClause.bindparams`
first with typing information, and a
second time with value information, and it will be combined::
stmt = text("SELECT id, name FROM user WHERE name=:name "
"AND timestamp=:timestamp")
stmt = stmt.bindparams(
bindparam('name', type_=String),
bindparam('timestamp', type_=DateTime)
)
stmt = stmt.bindparams(
name='jack',
timestamp=datetime.datetime(2012, 10, 8, 15, 12, 5)
)
The :meth:`_expression.TextClause.bindparams`
method also supports the concept of
**unique** bound parameters. These are parameters that are
"uniquified" on name at statement compilation time, so that multiple
:func:`_expression.text`
constructs may be combined together without the names
conflicting. To use this feature, specify the
:paramref:`.BindParameter.unique` flag on each :func:`.bindparam`
object::
stmt1 = text("select id from table where name=:name").bindparams(
bindparam("name", value='name1', unique=True)
)
stmt2 = text("select id from table where name=:name").bindparams(
bindparam("name", value='name2', unique=True)
)
union = union_all(
stmt1.columns(column("id")),
stmt2.columns(column("id"))
)
The above statement will render as::
select id from table where name=:name_1
UNION ALL select id from table where name=:name_2
.. versionadded:: 1.3.11 Added support for the
:paramref:`.BindParameter.unique` flag to work with
:func:`_expression.text`
constructs.
"""
self._bindparams = new_params = self._bindparams.copy()
for bind in binds:
try:
# the regex used for text() currently will not match
# a unique/anonymous key in any case, so use the _orig_key
# so that a text() construct can support unique parameters
existing = new_params[bind._orig_key]
except KeyError as err:
util.raise_(
exc.ArgumentError(
"This text() construct doesn't define a "
"bound parameter named %r" % bind._orig_key
),
replace_context=err,
)
else:
new_params[existing._orig_key] = bind
for key, value in names_to_values.items():
try:
existing = new_params[key]
except KeyError as err:
util.raise_(
exc.ArgumentError(
"This text() construct doesn't define a "
"bound parameter named %r" % key
),
replace_context=err,
)
else:
new_params[key] = existing._with_value(value)
@util.dependencies("sqlalchemy.sql.selectable")
def columns(self, selectable, *cols, **types):
"""Turn this :class:`_expression.TextClause` object into a
:class:`.TextAsFrom`
object that can be embedded into another statement.
This function essentially bridges the gap between an entirely
textual SELECT statement and the SQL expression language concept
of a "selectable"::
from sqlalchemy.sql import column, text
stmt = text("SELECT id, name FROM some_table")
stmt = stmt.columns(column('id'), column('name')).alias('st')
stmt = select([mytable]).\
select_from(
mytable.join(stmt, mytable.c.name == stmt.c.name)
).where(stmt.c.id > 5)
Above, we pass a series of :func:`_expression.column` elements to the
:meth:`_expression.TextClause.columns` method positionally. These
:func:`_expression.column`
elements now become first class elements upon the :attr:`.TextAsFrom.c`
column collection, just like any other selectable.
The column expressions we pass to
:meth:`_expression.TextClause.columns` may
also be typed; when we do so, these :class:`.TypeEngine` objects become
the effective return type of the column, so that SQLAlchemy's
result-set-processing systems may be used on the return values.
This is often needed for types such as date or boolean types, as well
as for unicode processing on some dialect configurations::
stmt = text("SELECT id, name, timestamp FROM some_table")
stmt = stmt.columns(
column('id', Integer),
column('name', Unicode),
column('timestamp', DateTime)
)
for id, name, timestamp in connection.execute(stmt):
print(id, name, timestamp)
As a shortcut to the above syntax, keyword arguments referring to
types alone may be used, if only type conversion is needed::
stmt = text("SELECT id, name, timestamp FROM some_table")
stmt = stmt.columns(
id=Integer,
name=Unicode,
timestamp=DateTime
)
for id, name, timestamp in connection.execute(stmt):
print(id, name, timestamp)
The positional form of :meth:`_expression.TextClause.columns`
also provides the
unique feature of **positional column targeting**, which is
particularly useful when using the ORM with complex textual queries. If
we specify the columns from our model to
:meth:`_expression.TextClause.columns`,
the result set will match to those columns positionally, meaning the
name or origin of the column in the textual SQL doesn't matter::
stmt = text("SELECT users.id, addresses.id, users.id, "
"users.name, addresses.email_address AS email "
"FROM users JOIN addresses ON users.id=addresses.user_id "
"WHERE users.id = 1").columns(
User.id,
Address.id,
Address.user_id,
User.name,
Address.email_address
)
query = session.query(User).from_statement(stmt).options(
contains_eager(User.addresses))
.. versionadded:: 1.1 the :meth:`_expression.TextClause.columns`
method now
offers positional column targeting in the result set when
the column expressions are passed purely positionally.
The :meth:`_expression.TextClause.columns` method provides a direct
route to calling :meth:`_expression.FromClause.alias` as well as
:meth:`_expression.SelectBase.cte`
against a textual SELECT statement::
stmt = stmt.columns(id=Integer, name=String).cte('st')
stmt = select([sometable]).where(sometable.c.id == stmt.c.id)
.. versionadded:: 0.9.0 :func:`_expression.text`
can now be converted into a
fully featured "selectable" construct using the
:meth:`_expression.TextClause.columns` method.
"""
positional_input_cols = [
ColumnClause(col.key, types.pop(col.key))
if col.key in types
else col
for col in cols
]
keyed_input_cols = [
ColumnClause(key, type_) for key, type_ in types.items()
]
return selectable.TextAsFrom(
self,
positional_input_cols + keyed_input_cols,
positional=bool(positional_input_cols) and not keyed_input_cols,
)
@property
def type(self):
return type_api.NULLTYPE
@property
def comparator(self):
return self.type.comparator_factory(self)
def self_group(self, against=None):
if against is operators.in_op:
return Grouping(self)
else:
return self
def _copy_internals(self, clone=_clone, **kw):
self._bindparams = dict(
(b.key, clone(b, **kw)) for b in self._bindparams.values()
)
def get_children(self, **kwargs):
return list(self._bindparams.values())
def compare(self, other):
return isinstance(other, TextClause) and other.text == self.text
class Null(ColumnElement):
"""Represent the NULL keyword in a SQL statement.
:class:`.Null` is accessed as a constant via the
:func:`.null` function.
"""
__visit_name__ = "null"
@util.memoized_property
def type(self):
return type_api.NULLTYPE
@classmethod
def _instance(cls):
"""Return a constant :class:`.Null` construct."""
return Null()
def compare(self, other):
return isinstance(other, Null)
class False_(ColumnElement):
"""Represent the ``false`` keyword, or equivalent, in a SQL statement.
:class:`.False_` is accessed as a constant via the
:func:`.false` function.
"""
__visit_name__ = "false"
@util.memoized_property
def type(self):
return type_api.BOOLEANTYPE
def _negate(self):
return True_()
@classmethod
def _instance(cls):
"""Return a :class:`.False_` construct.
E.g.::
>>> from sqlalchemy import false
>>> print(select([t.c.x]).where(false()))
SELECT x FROM t WHERE false
A backend which does not support true/false constants will render as
an expression against 1 or 0::
>>> print(select([t.c.x]).where(false()))
SELECT x FROM t WHERE 0 = 1
The :func:`.true` and :func:`.false` constants also feature
"short circuit" operation within an :func:`.and_` or :func:`.or_`
conjunction::
>>> print(select([t.c.x]).where(or_(t.c.x > 5, true())))
SELECT x FROM t WHERE true
>>> print(select([t.c.x]).where(and_(t.c.x > 5, false())))
SELECT x FROM t WHERE false
.. versionchanged:: 0.9 :func:`.true` and :func:`.false` feature
better integrated behavior within conjunctions and on dialects
that don't support true/false constants.
.. seealso::
:func:`.true`
"""
return False_()
def compare(self, other):
return isinstance(other, False_)
class True_(ColumnElement):
"""Represent the ``true`` keyword, or equivalent, in a SQL statement.
:class:`.True_` is accessed as a constant via the
:func:`.true` function.
"""
__visit_name__ = "true"
@util.memoized_property
def type(self):
return type_api.BOOLEANTYPE
def _negate(self):
return False_()
@classmethod
def _ifnone(cls, other):
if other is None:
return cls._instance()
else:
return other
@classmethod
def _instance(cls):
"""Return a constant :class:`.True_` construct.
E.g.::
>>> from sqlalchemy import true
>>> print(select([t.c.x]).where(true()))
SELECT x FROM t WHERE true
A backend which does not support true/false constants will render as
an expression against 1 or 0::
>>> print(select([t.c.x]).where(true()))
SELECT x FROM t WHERE 1 = 1
The :func:`.true` and :func:`.false` constants also feature
"short circuit" operation within an :func:`.and_` or :func:`.or_`
conjunction::
>>> print(select([t.c.x]).where(or_(t.c.x > 5, true())))
SELECT x FROM t WHERE true
>>> print(select([t.c.x]).where(and_(t.c.x > 5, false())))
SELECT x FROM t WHERE false
.. versionchanged:: 0.9 :func:`.true` and :func:`.false` feature
better integrated behavior within conjunctions and on dialects
that don't support true/false constants.
.. seealso::
:func:`.false`
"""
return True_()
def compare(self, other):
return isinstance(other, True_)
class ClauseList(ClauseElement):
"""Describe a list of clauses, separated by an operator.
By default, is comma-separated, such as a column listing.
"""
__visit_name__ = "clauselist"
def __init__(self, *clauses, **kwargs):
self.operator = kwargs.pop("operator", operators.comma_op)
self.group = kwargs.pop("group", True)
self.group_contents = kwargs.pop("group_contents", True)
self._tuple_values = kwargs.pop("_tuple_values", False)
text_converter = kwargs.pop(
"_literal_as_text", _expression_literal_as_text
)
if self.group_contents:
self.clauses = [
text_converter(clause).self_group(against=self.operator)
for clause in clauses
]
else:
self.clauses = [text_converter(clause) for clause in clauses]
self._is_implicitly_boolean = operators.is_boolean(self.operator)
def __iter__(self):
return iter(self.clauses)
def __len__(self):
return len(self.clauses)
@property
def _select_iterable(self):
return iter(self)
def append(self, clause):
if self.group_contents:
self.clauses.append(
_literal_as_text(clause).self_group(against=self.operator)
)
else:
self.clauses.append(_literal_as_text(clause))
def _copy_internals(self, clone=_clone, **kw):
self.clauses = [clone(clause, **kw) for clause in self.clauses]
def get_children(self, **kwargs):
return self.clauses
@property
def _from_objects(self):
return list(itertools.chain(*[c._from_objects for c in self.clauses]))
def self_group(self, against=None):
if self.group and operators.is_precedent(self.operator, against):
return Grouping(self)
else:
return self
def compare(self, other, **kw):
"""Compare this :class:`.ClauseList` to the given :class:`.ClauseList`,
including a comparison of all the clause items.
"""
if not isinstance(other, ClauseList) and len(self.clauses) == 1:
return self.clauses[0].compare(other, **kw)
elif (
isinstance(other, ClauseList)
and len(self.clauses) == len(other.clauses)
and self.operator is other.operator
):
if self.operator in (operators.and_, operators.or_):
completed = set()
for clause in self.clauses:
for other_clause in set(other.clauses).difference(
completed
):
if clause.compare(other_clause, **kw):
completed.add(other_clause)
break
return len(completed) == len(other.clauses)
else:
for i in range(0, len(self.clauses)):
if not self.clauses[i].compare(other.clauses[i], **kw):
return False
else:
return True
else:
return False
class BooleanClauseList(ClauseList, ColumnElement):
__visit_name__ = "clauselist"
_tuple_values = False
def __init__(self, *arg, **kw):
raise NotImplementedError(
"BooleanClauseList has a private constructor"
)
@classmethod
def _construct(cls, operator, continue_on, skip_on, *clauses, **kw):
convert_clauses = []
clauses = [
_expression_literal_as_text(clause)
for clause in util.coerce_generator_arg(clauses)
]
for clause in clauses:
if isinstance(clause, continue_on):
continue
elif isinstance(clause, skip_on):
return clause.self_group(against=operators._asbool)
convert_clauses.append(clause)
if len(convert_clauses) == 1:
return convert_clauses[0].self_group(against=operators._asbool)
elif not convert_clauses and clauses:
return clauses[0].self_group(against=operators._asbool)
convert_clauses = [
c.self_group(against=operator) for c in convert_clauses
]
self = cls.__new__(cls)
self.clauses = convert_clauses
self.group = True
self.operator = operator
self.group_contents = True
self.type = type_api.BOOLEANTYPE
self._is_implicitly_boolean = True
return self
@classmethod
def and_(cls, *clauses):
"""Produce a conjunction of expressions joined by ``AND``.
E.g.::
from sqlalchemy import and_
stmt = select([users_table]).where(
and_(
users_table.c.name == 'wendy',
users_table.c.enrolled == True
)
)
The :func:`.and_` conjunction is also available using the
Python ``&`` operator (though note that compound expressions
need to be parenthesized in order to function with Python
operator precedence behavior)::
stmt = select([users_table]).where(
(users_table.c.name == 'wendy') &
(users_table.c.enrolled == True)
)
The :func:`.and_` operation is also implicit in some cases;
the :meth:`_expression.Select.where`
method for example can be invoked multiple
times against a statement, which will have the effect of each
clause being combined using :func:`.and_`::
stmt = select([users_table]).\
where(users_table.c.name == 'wendy').\
where(users_table.c.enrolled == True)
.. seealso::
:func:`.or_`
"""
return cls._construct(operators.and_, True_, False_, *clauses)
@classmethod
def or_(cls, *clauses):
"""Produce a conjunction of expressions joined by ``OR``.
E.g.::
from sqlalchemy import or_
stmt = select([users_table]).where(
or_(
users_table.c.name == 'wendy',
users_table.c.name == 'jack'
)
)
The :func:`.or_` conjunction is also available using the
Python ``|`` operator (though note that compound expressions
need to be parenthesized in order to function with Python
operator precedence behavior)::
stmt = select([users_table]).where(
(users_table.c.name == 'wendy') |
(users_table.c.name == 'jack')
)
.. seealso::
:func:`.and_`
"""
return cls._construct(operators.or_, False_, True_, *clauses)
@property
def _select_iterable(self):
return (self,)
def self_group(self, against=None):
if not self.clauses:
return self
else:
return super(BooleanClauseList, self).self_group(against=against)
def _negate(self):
return ClauseList._negate(self)
and_ = BooleanClauseList.and_
or_ = BooleanClauseList.or_
class Tuple(ClauseList, ColumnElement):
"""Represent a SQL tuple."""
def __init__(self, *clauses, **kw):
"""Return a :class:`.Tuple`.
Main usage is to produce a composite IN construct using
:meth:`.ColumnOperators.in_` ::
from sqlalchemy import tuple_
tuple_(table.c.col1, table.c.col2).in_(
[(1, 2), (5, 12), (10, 19)]
)
.. versionchanged:: 1.3.6 Added support for SQLite IN tuples.
.. warning::
The composite IN construct is not supported by all backends, and is
currently known to work on PostgreSQL, MySQL, and SQLite.
Unsupported backends will raise a subclass of
:class:`~sqlalchemy.exc.DBAPIError` when such an expression is
invoked.
"""
clauses = [_literal_as_binds(c) for c in clauses]
self._type_tuple = [arg.type for arg in clauses]
self.type = kw.pop(
"type_",
self._type_tuple[0] if self._type_tuple else type_api.NULLTYPE,
)
super(Tuple, self).__init__(*clauses, **kw)
@property
def _select_iterable(self):
return (self,)
def _bind_param(self, operator, obj, type_=None):
return Tuple(
*[
BindParameter(
None,
o,
_compared_to_operator=operator,
_compared_to_type=compared_to_type,
unique=True,
type_=type_,
)
for o, compared_to_type in zip(obj, self._type_tuple)
]
).self_group()
class Case(ColumnElement):
"""Represent a ``CASE`` expression.
:class:`.Case` is produced using the :func:`.case` factory function,
as in::
from sqlalchemy import case
stmt = select([users_table]).\
where(
case(
[
(users_table.c.name == 'wendy', 'W'),
(users_table.c.name == 'jack', 'J')
],
else_='E'
)
)
Details on :class:`.Case` usage is at :func:`.case`.
.. seealso::
:func:`.case`
"""
__visit_name__ = "case"
def __init__(self, whens, value=None, else_=None):
r"""Produce a ``CASE`` expression.
The ``CASE`` construct in SQL is a conditional object that
acts somewhat analogously to an "if/then" construct in other
languages. It returns an instance of :class:`.Case`.
:func:`.case` in its usual form is passed a list of "when"
constructs, that is, a list of conditions and results as tuples::
from sqlalchemy import case
stmt = select([users_table]).\
where(
case(
[
(users_table.c.name == 'wendy', 'W'),
(users_table.c.name == 'jack', 'J')
],
else_='E'
)
)
The above statement will produce SQL resembling::
SELECT id, name FROM user
WHERE CASE
WHEN (name = :name_1) THEN :param_1
WHEN (name = :name_2) THEN :param_2
ELSE :param_3
END
When simple equality expressions of several values against a single
parent column are needed, :func:`.case` also has a "shorthand" format
used via the
:paramref:`.case.value` parameter, which is passed a column
expression to be compared. In this form, the :paramref:`.case.whens`
parameter is passed as a dictionary containing expressions to be
compared against keyed to result expressions. The statement below is
equivalent to the preceding statement::
stmt = select([users_table]).\
where(
case(
{"wendy": "W", "jack": "J"},
value=users_table.c.name,
else_='E'
)
)
The values which are accepted as result values in
:paramref:`.case.whens` as well as with :paramref:`.case.else_` are
coerced from Python literals into :func:`.bindparam` constructs.
SQL expressions, e.g. :class:`_expression.ColumnElement` constructs,
are accepted
as well. To coerce a literal string expression into a constant
expression rendered inline, use the :func:`_expression.literal_column`
construct,
as in::
from sqlalchemy import case, literal_column
case(
[
(
orderline.c.qty > 100,
literal_column("'greaterthan100'")
),
(
orderline.c.qty > 10,
literal_column("'greaterthan10'")
)
],
else_=literal_column("'lessthan10'")
)
The above will render the given constants without using bound
parameters for the result values (but still for the comparison
values), as in::
CASE
WHEN (orderline.qty > :qty_1) THEN 'greaterthan100'
WHEN (orderline.qty > :qty_2) THEN 'greaterthan10'
ELSE 'lessthan10'
END
:param whens: The criteria to be compared against,
:paramref:`.case.whens` accepts two different forms, based on
whether or not :paramref:`.case.value` is used.
In the first form, it accepts a list of 2-tuples; each 2-tuple
consists of ``(<sql expression>, <value>)``, where the SQL
expression is a boolean expression and "value" is a resulting value,
e.g.::
case([
(users_table.c.name == 'wendy', 'W'),
(users_table.c.name == 'jack', 'J')
])
In the second form, it accepts a Python dictionary of comparison
values mapped to a resulting value; this form requires
:paramref:`.case.value` to be present, and values will be compared
using the ``==`` operator, e.g.::
case(
{"wendy": "W", "jack": "J"},
value=users_table.c.name
)
:param value: An optional SQL expression which will be used as a
fixed "comparison point" for candidate values within a dictionary
passed to :paramref:`.case.whens`.
:param else\_: An optional SQL expression which will be the evaluated
result of the ``CASE`` construct if all expressions within
:paramref:`.case.whens` evaluate to false. When omitted, most
databases will produce a result of NULL if none of the "when"
expressions evaluate to true.
"""
try:
whens = util.dictlike_iteritems(whens)
except TypeError:
pass
if value is not None:
whenlist = [
(_literal_as_binds(c).self_group(), _literal_as_binds(r))
for (c, r) in whens
]
else:
whenlist = [
(_no_literals(c).self_group(), _literal_as_binds(r))
for (c, r) in whens
]
if whenlist:
type_ = list(whenlist[-1])[-1].type
else:
type_ = None
if value is None:
self.value = None
else:
self.value = _literal_as_binds(value)
self.type = type_
self.whens = whenlist
if else_ is not None:
self.else_ = _literal_as_binds(else_)
else:
self.else_ = None
def _copy_internals(self, clone=_clone, **kw):
if self.value is not None:
self.value = clone(self.value, **kw)
self.whens = [(clone(x, **kw), clone(y, **kw)) for x, y in self.whens]
if self.else_ is not None:
self.else_ = clone(self.else_, **kw)
def get_children(self, **kwargs):
if self.value is not None:
yield self.value
for x, y in self.whens:
yield x
yield y
if self.else_ is not None:
yield self.else_
@property
def _from_objects(self):
return list(
itertools.chain(*[x._from_objects for x in self.get_children()])
)
def literal_column(text, type_=None):
r"""Produce a :class:`.ColumnClause` object that has the
:paramref:`_expression.column.is_literal` flag set to True.
:func:`_expression.literal_column` is similar to
:func:`_expression.column`, except that
it is more often used as a "standalone" column expression that renders
exactly as stated; while :func:`_expression.column`
stores a string name that
will be assumed to be part of a table and may be quoted as such,
:func:`_expression.literal_column` can be that,
or any other arbitrary column-oriented
expression.
:param text: the text of the expression; can be any SQL expression.
Quoting rules will not be applied. To specify a column-name expression
which should be subject to quoting rules, use the :func:`column`
function.
:param type\_: an optional :class:`~sqlalchemy.types.TypeEngine`
object which will
provide result-set translation and additional expression semantics for
this column. If left as None the type will be NullType.
.. seealso::
:func:`_expression.column`
:func:`_expression.text`
:ref:`sqlexpression_literal_column`
"""
return ColumnClause(text, type_=type_, is_literal=True)
class Cast(ColumnElement):
"""Represent a ``CAST`` expression.
:class:`.Cast` is produced using the :func:`.cast` factory function,
as in::
from sqlalchemy import cast, Numeric
stmt = select([
cast(product_table.c.unit_price, Numeric(10, 4))
])
Details on :class:`.Cast` usage is at :func:`.cast`.
.. seealso::
:ref:`coretutorial_casts`
:func:`.cast`
:func:`.type_coerce` - an alternative to CAST that coerces the type
on the Python side only, which is often sufficient to generate the
correct SQL and data coercion.
"""
__visit_name__ = "cast"
def __init__(self, expression, type_):
r"""Produce a ``CAST`` expression.
:func:`.cast` returns an instance of :class:`.Cast`.
E.g.::
from sqlalchemy import cast, Numeric
stmt = select([
cast(product_table.c.unit_price, Numeric(10, 4))
])
The above statement will produce SQL resembling::
SELECT CAST(unit_price AS NUMERIC(10, 4)) FROM product
The :func:`.cast` function performs two distinct functions when
used. The first is that it renders the ``CAST`` expression within
the resulting SQL string. The second is that it associates the given
type (e.g. :class:`.TypeEngine` class or instance) with the column
expression on the Python side, which means the expression will take
on the expression operator behavior associated with that type,
as well as the bound-value handling and result-row-handling behavior
of the type.
.. versionchanged:: 0.9.0 :func:`.cast` now applies the given type
to the expression such that it takes effect on the bound-value,
e.g. the Python-to-database direction, in addition to the
result handling, e.g. database-to-Python, direction.
An alternative to :func:`.cast` is the :func:`.type_coerce` function.
This function performs the second task of associating an expression
with a specific type, but does not render the ``CAST`` expression
in SQL.
:param expression: A SQL expression, such as a
:class:`_expression.ColumnElement`
expression or a Python string which will be coerced into a bound
literal value.
:param type\_: A :class:`.TypeEngine` class or instance indicating
the type to which the ``CAST`` should apply.
.. seealso::
:ref:`coretutorial_casts`
:func:`.type_coerce` - an alternative to CAST that coerces the type
on the Python side only, which is often sufficient to generate the
correct SQL and data coercion.
"""
self.type = type_api.to_instance(type_)
self.clause = _literal_as_binds(expression, type_=self.type)
self.typeclause = TypeClause(self.type)
def _copy_internals(self, clone=_clone, **kw):
self.clause = clone(self.clause, **kw)
self.typeclause = clone(self.typeclause, **kw)
def get_children(self, **kwargs):
return self.clause, self.typeclause
@property
def _from_objects(self):
return self.clause._from_objects
class TypeCoerce(ColumnElement):
"""Represent a Python-side type-coercion wrapper.
:class:`.TypeCoerce` supplies the :func:`_expression.type_coerce`
function; see that function for usage details.
.. versionchanged:: 1.1 The :func:`.type_coerce` function now produces
a persistent :class:`.TypeCoerce` wrapper object rather than
translating the given object in place.
.. seealso::
:func:`_expression.type_coerce`
:func:`.cast`
"""
__visit_name__ = "type_coerce"
def __init__(self, expression, type_):
r"""Associate a SQL expression with a particular type, without rendering
``CAST``.
E.g.::
from sqlalchemy import type_coerce
stmt = select([
type_coerce(log_table.date_string, StringDateTime())
])
The above construct will produce a :class:`.TypeCoerce` object, which
renders SQL that labels the expression, but otherwise does not
modify its value on the SQL side::
SELECT date_string AS anon_1 FROM log
When result rows are fetched, the ``StringDateTime`` type
will be applied to result rows on behalf of the ``date_string`` column.
The rationale for the "anon_1" label is so that the type-coerced
column remains separate in the list of result columns vs. other
type-coerced or direct values of the target column. In order to
provide a named label for the expression, use
:meth:`_expression.ColumnElement.label`::
stmt = select([
type_coerce(
log_table.date_string, StringDateTime()).label('date')
])
A type that features bound-value handling will also have that behavior
take effect when literal values or :func:`.bindparam` constructs are
passed to :func:`.type_coerce` as targets.
For example, if a type implements the
:meth:`.TypeEngine.bind_expression`
method or :meth:`.TypeEngine.bind_processor` method or equivalent,
these functions will take effect at statement compilation/execution
time when a literal value is passed, as in::
# bound-value handling of MyStringType will be applied to the
# literal value "some string"
stmt = select([type_coerce("some string", MyStringType)])
:func:`.type_coerce` is similar to the :func:`.cast` function,
except that it does not render the ``CAST`` expression in the resulting
statement.
:param expression: A SQL expression, such as a
:class:`_expression.ColumnElement`
expression or a Python string which will be coerced into a bound
literal value.
:param type\_: A :class:`.TypeEngine` class or instance indicating
the type to which the expression is coerced.
.. seealso::
:ref:`coretutorial_casts`
:func:`.cast`
"""
self.type = type_api.to_instance(type_)
self.clause = _literal_as_binds(expression, type_=self.type)
def _copy_internals(self, clone=_clone, **kw):
self.clause = clone(self.clause, **kw)
self.__dict__.pop("typed_expression", None)
def get_children(self, **kwargs):
return (self.clause,)
@property
def _from_objects(self):
return self.clause._from_objects
@util.memoized_property
def typed_expression(self):
if isinstance(self.clause, BindParameter):
bp = self.clause._clone()
bp.type = self.type
return bp
else:
return self.clause
class Extract(ColumnElement):
"""Represent a SQL EXTRACT clause, ``extract(field FROM expr)``."""
__visit_name__ = "extract"
def __init__(self, field, expr, **kwargs):
"""Return a :class:`.Extract` construct.
This is typically available as :func:`.extract`
as well as ``func.extract`` from the
:data:`.func` namespace.
"""
self.type = type_api.INTEGERTYPE
self.field = field
self.expr = _literal_as_binds(expr, None)
def _copy_internals(self, clone=_clone, **kw):
self.expr = clone(self.expr, **kw)
def get_children(self, **kwargs):
return (self.expr,)
@property
def _from_objects(self):
return self.expr._from_objects
class _label_reference(ColumnElement):
"""Wrap a column expression as it appears in a 'reference' context.
This expression is any that includes an _order_by_label_element,
which is a Label, or a DESC / ASC construct wrapping a Label.
The production of _label_reference() should occur when an expression
is added to this context; this includes the ORDER BY or GROUP BY of a
SELECT statement, as well as a few other places, such as the ORDER BY
within an OVER clause.
"""
__visit_name__ = "label_reference"
def __init__(self, element):
self.element = element
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
@property
def _from_objects(self):
return ()
class _textual_label_reference(ColumnElement):
__visit_name__ = "textual_label_reference"
def __init__(self, element):
self.element = element
@util.memoized_property
def _text_clause(self):
return TextClause._create_text(self.element)
class UnaryExpression(ColumnElement):
"""Define a 'unary' expression.
A unary expression has a single column expression
and an operator. The operator can be placed on the left
(where it is called the 'operator') or right (where it is called the
'modifier') of the column expression.
:class:`.UnaryExpression` is the basis for several unary operators
including those used by :func:`.desc`, :func:`.asc`, :func:`.distinct`,
:func:`.nullsfirst` and :func:`.nullslast`.
"""
__visit_name__ = "unary"
def __init__(
self,
element,
operator=None,
modifier=None,
type_=None,
negate=None,
wraps_column_expression=False,
):
self.operator = operator
self.modifier = modifier
self.element = element.self_group(
against=self.operator or self.modifier
)
self.type = type_api.to_instance(type_)
self.negate = negate
self.wraps_column_expression = wraps_column_expression
@classmethod
def _create_nullsfirst(cls, column):
"""Produce the ``NULLS FIRST`` modifier for an ``ORDER BY`` expression.
:func:`.nullsfirst` is intended to modify the expression produced
by :func:`.asc` or :func:`.desc`, and indicates how NULL values
should be handled when they are encountered during ordering::
from sqlalchemy import desc, nullsfirst
stmt = select([users_table]).\
order_by(nullsfirst(desc(users_table.c.name)))
The SQL expression from the above would resemble::
SELECT id, name FROM user ORDER BY name DESC NULLS FIRST
Like :func:`.asc` and :func:`.desc`, :func:`.nullsfirst` is typically
invoked from the column expression itself using
:meth:`_expression.ColumnElement.nullsfirst`,
rather than as its standalone
function version, as in::
stmt = (select([users_table]).
order_by(users_table.c.name.desc().nullsfirst())
)
.. seealso::
:func:`.asc`
:func:`.desc`
:func:`.nullslast`
:meth:`_expression.Select.order_by`
"""
return UnaryExpression(
_literal_as_label_reference(column),
modifier=operators.nullsfirst_op,
wraps_column_expression=False,
)
@classmethod
def _create_nullslast(cls, column):
"""Produce the ``NULLS LAST`` modifier for an ``ORDER BY`` expression.
:func:`.nullslast` is intended to modify the expression produced
by :func:`.asc` or :func:`.desc`, and indicates how NULL values
should be handled when they are encountered during ordering::
from sqlalchemy import desc, nullslast
stmt = select([users_table]).\
order_by(nullslast(desc(users_table.c.name)))
The SQL expression from the above would resemble::
SELECT id, name FROM user ORDER BY name DESC NULLS LAST
Like :func:`.asc` and :func:`.desc`, :func:`.nullslast` is typically
invoked from the column expression itself using
:meth:`_expression.ColumnElement.nullslast`,
rather than as its standalone
function version, as in::
stmt = select([users_table]).\
order_by(users_table.c.name.desc().nullslast())
.. seealso::
:func:`.asc`
:func:`.desc`
:func:`.nullsfirst`
:meth:`_expression.Select.order_by`
"""
return UnaryExpression(
_literal_as_label_reference(column),
modifier=operators.nullslast_op,
wraps_column_expression=False,
)
@classmethod
def _create_desc(cls, column):
"""Produce a descending ``ORDER BY`` clause element.
e.g.::
from sqlalchemy import desc
stmt = select([users_table]).order_by(desc(users_table.c.name))
will produce SQL as::
SELECT id, name FROM user ORDER BY name DESC
The :func:`.desc` function is a standalone version of the
:meth:`_expression.ColumnElement.desc`
method available on all SQL expressions,
e.g.::
stmt = select([users_table]).order_by(users_table.c.name.desc())
:param column: A :class:`_expression.ColumnElement` (e.g.
scalar SQL expression)
with which to apply the :func:`.desc` operation.
.. seealso::
:func:`.asc`
:func:`.nullsfirst`
:func:`.nullslast`
:meth:`_expression.Select.order_by`
"""
return UnaryExpression(
_literal_as_label_reference(column),
modifier=operators.desc_op,
wraps_column_expression=False,
)
@classmethod
def _create_asc(cls, column):
"""Produce an ascending ``ORDER BY`` clause element.
e.g.::
from sqlalchemy import asc
stmt = select([users_table]).order_by(asc(users_table.c.name))
will produce SQL as::
SELECT id, name FROM user ORDER BY name ASC
The :func:`.asc` function is a standalone version of the
:meth:`_expression.ColumnElement.asc`
method available on all SQL expressions,
e.g.::
stmt = select([users_table]).order_by(users_table.c.name.asc())
:param column: A :class:`_expression.ColumnElement` (e.g.
scalar SQL expression)
with which to apply the :func:`.asc` operation.
.. seealso::
:func:`.desc`
:func:`.nullsfirst`
:func:`.nullslast`
:meth:`_expression.Select.order_by`
"""
return UnaryExpression(
_literal_as_label_reference(column),
modifier=operators.asc_op,
wraps_column_expression=False,
)
@classmethod
def _create_distinct(cls, expr):
"""Produce an column-expression-level unary ``DISTINCT`` clause.
This applies the ``DISTINCT`` keyword to an individual column
expression, and is typically contained within an aggregate function,
as in::
from sqlalchemy import distinct, func
stmt = select([func.count(distinct(users_table.c.name))])
The above would produce an expression resembling::
SELECT COUNT(DISTINCT name) FROM user
The :func:`.distinct` function is also available as a column-level
method, e.g. :meth:`_expression.ColumnElement.distinct`, as in::
stmt = select([func.count(users_table.c.name.distinct())])
The :func:`.distinct` operator is different from the
:meth:`_expression.Select.distinct` method of
:class:`_expression.Select`,
which produces a ``SELECT`` statement
with ``DISTINCT`` applied to the result set as a whole,
e.g. a ``SELECT DISTINCT`` expression. See that method for further
information.
.. seealso::
:meth:`_expression.ColumnElement.distinct`
:meth:`_expression.Select.distinct`
:data:`.func`
"""
expr = _literal_as_binds(expr)
return UnaryExpression(
expr,
operator=operators.distinct_op,
type_=expr.type,
wraps_column_expression=False,
)
@property
def _order_by_label_element(self):
if self.modifier in (operators.desc_op, operators.asc_op):
return self.element._order_by_label_element
else:
return None
@property
def _from_objects(self):
return self.element._from_objects
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
def get_children(self, **kwargs):
return (self.element,)
def compare(self, other, **kw):
"""Compare this :class:`UnaryExpression` against the given
:class:`_expression.ClauseElement`."""
return (
isinstance(other, UnaryExpression)
and self.operator == other.operator
and self.modifier == other.modifier
and self.element.compare(other.element, **kw)
)
def _negate(self):
if self.negate is not None:
return UnaryExpression(
self.element,
operator=self.negate,
negate=self.operator,
modifier=self.modifier,
type_=self.type,
wraps_column_expression=self.wraps_column_expression,
)
elif self.type._type_affinity is type_api.BOOLEANTYPE._type_affinity:
return UnaryExpression(
self.self_group(against=operators.inv),
operator=operators.inv,
type_=type_api.BOOLEANTYPE,
wraps_column_expression=self.wraps_column_expression,
negate=None,
)
else:
return ClauseElement._negate(self)
def self_group(self, against=None):
if self.operator and operators.is_precedent(self.operator, against):
return Grouping(self)
else:
return self
class CollectionAggregate(UnaryExpression):
"""Forms the basis for right-hand collection operator modifiers
ANY and ALL.
The ANY and ALL keywords are available in different ways on different
backends. On PostgreSQL, they only work for an ARRAY type. On
MySQL, they only work for subqueries.
"""
@classmethod
def _create_any(cls, expr):
"""Produce an ANY expression.
This may apply to an array type for some dialects (e.g. postgresql),
or to a subquery for others (e.g. mysql). e.g.::
# postgresql '5 = ANY (somearray)'
expr = 5 == any_(mytable.c.somearray)
# mysql '5 = ANY (SELECT value FROM table)'
expr = 5 == any_(select([table.c.value]))
.. versionadded:: 1.1
.. seealso::
:func:`_expression.all_`
"""
expr = _literal_as_binds(expr)
if expr.is_selectable and hasattr(expr, "as_scalar"):
expr = expr.as_scalar()
expr = expr.self_group()
return CollectionAggregate(
expr,
operator=operators.any_op,
type_=type_api.NULLTYPE,
wraps_column_expression=False,
)
@classmethod
def _create_all(cls, expr):
"""Produce an ALL expression.
This may apply to an array type for some dialects (e.g. postgresql),
or to a subquery for others (e.g. mysql). e.g.::
# postgresql '5 = ALL (somearray)'
expr = 5 == all_(mytable.c.somearray)
# mysql '5 = ALL (SELECT value FROM table)'
expr = 5 == all_(select([table.c.value]))
.. versionadded:: 1.1
.. seealso::
:func:`_expression.any_`
"""
expr = _literal_as_binds(expr)
if expr.is_selectable and hasattr(expr, "as_scalar"):
expr = expr.as_scalar()
expr = expr.self_group()
return CollectionAggregate(
expr,
operator=operators.all_op,
type_=type_api.NULLTYPE,
wraps_column_expression=False,
)
# operate and reverse_operate are hardwired to
# dispatch onto the type comparator directly, so that we can
# ensure "reversed" behavior.
def operate(self, op, *other, **kwargs):
if not operators.is_comparison(op):
raise exc.ArgumentError(
"Only comparison operators may be used with ANY/ALL"
)
kwargs["reverse"] = True
return self.comparator.operate(operators.mirror(op), *other, **kwargs)
def reverse_operate(self, op, other, **kwargs):
# comparison operators should never call reverse_operate
assert not operators.is_comparison(op)
raise exc.ArgumentError(
"Only comparison operators may be used with ANY/ALL"
)
class AsBoolean(UnaryExpression):
def __init__(self, element, operator, negate):
self.element = element
self.type = type_api.BOOLEANTYPE
self.operator = operator
self.negate = negate
self.modifier = None
self.wraps_column_expression = True
self._is_implicitly_boolean = element._is_implicitly_boolean
def self_group(self, against=None):
return self
def _negate(self):
if isinstance(self.element, (True_, False_)):
return self.element._negate()
else:
return AsBoolean(self.element, self.negate, self.operator)
class BinaryExpression(ColumnElement):
"""Represent an expression that is ``LEFT <operator> RIGHT``.
A :class:`.BinaryExpression` is generated automatically
whenever two column expressions are used in a Python binary expression::
>>> from sqlalchemy.sql import column
>>> column('a') + column('b')
<sqlalchemy.sql.expression.BinaryExpression object at 0x101029dd0>
>>> print(column('a') + column('b'))
a + b
"""
__visit_name__ = "binary"
_is_implicitly_boolean = True
"""Indicates that any database will know this is a boolean expression
even if the database does not have an explicit boolean datatype.
"""
def __init__(
self, left, right, operator, type_=None, negate=None, modifiers=None
):
# allow compatibility with libraries that
# refer to BinaryExpression directly and pass strings
if isinstance(operator, util.string_types):
operator = operators.custom_op(operator)
self._orig = (left, right)
self.left = left.self_group(against=operator)
self.right = right.self_group(against=operator)
self.operator = operator
self.type = type_api.to_instance(type_)
self.negate = negate
self._is_implicitly_boolean = operators.is_boolean(operator)
if modifiers is None:
self.modifiers = {}
else:
self.modifiers = modifiers
def __bool__(self):
if self.operator in (operator.eq, operator.ne):
return self.operator(hash(self._orig[0]), hash(self._orig[1]))
else:
raise TypeError("Boolean value of this clause is not defined")
__nonzero__ = __bool__
@property
def is_comparison(self):
return operators.is_comparison(self.operator)
@property
def _from_objects(self):
return self.left._from_objects + self.right._from_objects
def _copy_internals(self, clone=_clone, **kw):
self.left = clone(self.left, **kw)
self.right = clone(self.right, **kw)
def get_children(self, **kwargs):
return self.left, self.right
def compare(self, other, **kw):
"""Compare this :class:`BinaryExpression` against the
given :class:`BinaryExpression`."""
return (
isinstance(other, BinaryExpression)
and self.operator == other.operator
and (
self.left.compare(other.left, **kw)
and self.right.compare(other.right, **kw)
or (
operators.is_commutative(self.operator)
and self.left.compare(other.right, **kw)
and self.right.compare(other.left, **kw)
)
)
)
def self_group(self, against=None):
if operators.is_precedent(self.operator, against):
return Grouping(self)
else:
return self
def _negate(self):
if self.negate is not None:
return BinaryExpression(
self.left,
self.right,
self.negate,
negate=self.operator,
type_=self.type,
modifiers=self.modifiers,
)
else:
return super(BinaryExpression, self)._negate()
class Slice(ColumnElement):
"""Represent SQL for a Python array-slice object.
This is not a specific SQL construct at this level, but
may be interpreted by specific dialects, e.g. PostgreSQL.
"""
__visit_name__ = "slice"
def __init__(self, start, stop, step):
self.start = start
self.stop = stop
self.step = step
self.type = type_api.NULLTYPE
def self_group(self, against=None):
assert against is operator.getitem
return self
class IndexExpression(BinaryExpression):
"""Represent the class of expressions that are like an "index" operation.
"""
pass
class Grouping(ColumnElement):
"""Represent a grouping within a column expression"""
__visit_name__ = "grouping"
def __init__(self, element):
self.element = element
self.type = getattr(element, "type", type_api.NULLTYPE)
def self_group(self, against=None):
return self
@util.memoized_property
def _is_implicitly_boolean(self):
return self.element._is_implicitly_boolean
@property
def _key_label(self):
return self._label
@property
def _label(self):
return getattr(self.element, "_label", None) or self.anon_label
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
def get_children(self, **kwargs):
return (self.element,)
@property
def _from_objects(self):
return self.element._from_objects
def __getattr__(self, attr):
return getattr(self.element, attr)
def __getstate__(self):
return {"element": self.element, "type": self.type}
def __setstate__(self, state):
self.element = state["element"]
self.type = state["type"]
def compare(self, other, **kw):
return isinstance(other, Grouping) and self.element.compare(
other.element
)
RANGE_UNBOUNDED = util.symbol("RANGE_UNBOUNDED")
RANGE_CURRENT = util.symbol("RANGE_CURRENT")
class Over(ColumnElement):
"""Represent an OVER clause.
This is a special operator against a so-called
"window" function, as well as any aggregate function,
which produces results relative to the result set
itself. It's supported only by certain database
backends.
"""
__visit_name__ = "over"
order_by = None
partition_by = None
element = None
"""The underlying expression object to which this :class:`.Over`
object refers towards."""
def __init__(
self, element, partition_by=None, order_by=None, range_=None, rows=None
):
r"""Produce an :class:`.Over` object against a function.
Used against aggregate or so-called "window" functions,
for database backends that support window functions.
:func:`_expression.over` is usually called using
the :meth:`.FunctionElement.over` method, e.g.::
func.row_number().over(order_by=mytable.c.some_column)
Would produce::
ROW_NUMBER() OVER(ORDER BY some_column)
Ranges are also possible using the :paramref:`.expression.over.range_`
and :paramref:`.expression.over.rows` parameters. These
mutually-exclusive parameters each accept a 2-tuple, which contains
a combination of integers and None::
func.row_number().over(
order_by=my_table.c.some_column, range_=(None, 0))
The above would produce::
ROW_NUMBER() OVER(ORDER BY some_column
RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
A value of None indicates "unbounded", a
value of zero indicates "current row", and negative / positive
integers indicate "preceding" and "following":
* RANGE BETWEEN 5 PRECEDING AND 10 FOLLOWING::
func.row_number().over(order_by='x', range_=(-5, 10))
* ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW::
func.row_number().over(order_by='x', rows=(None, 0))
* RANGE BETWEEN 2 PRECEDING AND UNBOUNDED FOLLOWING::
func.row_number().over(order_by='x', range_=(-2, None))
* RANGE BETWEEN 1 FOLLOWING AND 3 FOLLOWING::
func.row_number().over(order_by='x', range_=(1, 3))
.. versionadded:: 1.1 support for RANGE / ROWS within a window
:param element: a :class:`.FunctionElement`, :class:`.WithinGroup`,
or other compatible construct.
:param partition_by: a column element or string, or a list
of such, that will be used as the PARTITION BY clause
of the OVER construct.
:param order_by: a column element or string, or a list
of such, that will be used as the ORDER BY clause
of the OVER construct.
:param range\_: optional range clause for the window. This is a
tuple value which can contain integer values or None, and will
render a RANGE BETWEEN PRECEDING / FOLLOWING clause
.. versionadded:: 1.1
:param rows: optional rows clause for the window. This is a tuple
value which can contain integer values or None, and will render
a ROWS BETWEEN PRECEDING / FOLLOWING clause.
.. versionadded:: 1.1
This function is also available from the :data:`~.expression.func`
construct itself via the :meth:`.FunctionElement.over` method.
.. seealso::
:data:`.expression.func`
:func:`_expression.within_group`
"""
self.element = element
if order_by is not None:
self.order_by = ClauseList(
*util.to_list(order_by),
_literal_as_text=_literal_as_label_reference
)
if partition_by is not None:
self.partition_by = ClauseList(
*util.to_list(partition_by),
_literal_as_text=_literal_as_label_reference
)
if range_:
self.range_ = self._interpret_range(range_)
if rows:
raise exc.ArgumentError(
"'range_' and 'rows' are mutually exclusive"
)
else:
self.rows = None
elif rows:
self.rows = self._interpret_range(rows)
self.range_ = None
else:
self.rows = self.range_ = None
def _interpret_range(self, range_):
if not isinstance(range_, tuple) or len(range_) != 2:
raise exc.ArgumentError("2-tuple expected for range/rows")
if range_[0] is None:
lower = RANGE_UNBOUNDED
else:
try:
lower = int(range_[0])
except ValueError as err:
util.raise_(
exc.ArgumentError(
"Integer or None expected for range value"
),
replace_context=err,
)
else:
if lower == 0:
lower = RANGE_CURRENT
if range_[1] is None:
upper = RANGE_UNBOUNDED
else:
try:
upper = int(range_[1])
except ValueError as err:
util.raise_(
exc.ArgumentError(
"Integer or None expected for range value"
),
replace_context=err,
)
else:
if upper == 0:
upper = RANGE_CURRENT
return lower, upper
@property
@util.deprecated(
"1.1",
"the :attr:`.Over.func` member of the :class:`.Over` "
"class is deprecated and will be removed in a future release. "
"Please refer to the :attr:`.Over.element` attribute.",
)
def func(self):
"""the element referred to by this :class:`.Over`
clause.
"""
return self.element
@util.memoized_property
def type(self):
return self.element.type
def get_children(self, **kwargs):
return [
c
for c in (self.element, self.partition_by, self.order_by)
if c is not None
]
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
if self.partition_by is not None:
self.partition_by = clone(self.partition_by, **kw)
if self.order_by is not None:
self.order_by = clone(self.order_by, **kw)
@property
def _from_objects(self):
return list(
itertools.chain(
*[
c._from_objects
for c in (self.element, self.partition_by, self.order_by)
if c is not None
]
)
)
class WithinGroup(ColumnElement):
"""Represent a WITHIN GROUP (ORDER BY) clause.
This is a special operator against so-called
"ordered set aggregate" and "hypothetical
set aggregate" functions, including ``percentile_cont()``,
``rank()``, ``dense_rank()``, etc.
It's supported only by certain database backends, such as PostgreSQL,
Oracle and MS SQL Server.
The :class:`.WithinGroup` construct extracts its type from the
method :meth:`.FunctionElement.within_group_type`. If this returns
``None``, the function's ``.type`` is used.
"""
__visit_name__ = "withingroup"
order_by = None
def __init__(self, element, *order_by):
r"""Produce a :class:`.WithinGroup` object against a function.
Used against so-called "ordered set aggregate" and "hypothetical
set aggregate" functions, including :class:`.percentile_cont`,
:class:`.rank`, :class:`.dense_rank`, etc.
:func:`_expression.within_group` is usually called using
the :meth:`.FunctionElement.within_group` method, e.g.::
from sqlalchemy import within_group
stmt = select([
department.c.id,
func.percentile_cont(0.5).within_group(
department.c.salary.desc()
)
])
The above statement would produce SQL similar to
``SELECT department.id, percentile_cont(0.5)
WITHIN GROUP (ORDER BY department.salary DESC)``.
:param element: a :class:`.FunctionElement` construct, typically
generated by :data:`~.expression.func`.
:param \*order_by: one or more column elements that will be used
as the ORDER BY clause of the WITHIN GROUP construct.
.. versionadded:: 1.1
.. seealso::
:data:`.expression.func`
:func:`_expression.over`
"""
self.element = element
if order_by is not None:
self.order_by = ClauseList(
*util.to_list(order_by),
_literal_as_text=_literal_as_label_reference
)
def over(self, partition_by=None, order_by=None, range_=None, rows=None):
"""Produce an OVER clause against this :class:`.WithinGroup`
construct.
This function has the same signature as that of
:meth:`.FunctionElement.over`.
"""
return Over(
self,
partition_by=partition_by,
order_by=order_by,
range_=range_,
rows=rows,
)
@util.memoized_property
def type(self):
wgt = self.element.within_group_type(self)
if wgt is not None:
return wgt
else:
return self.element.type
def get_children(self, **kwargs):
return [c for c in (self.element, self.order_by) if c is not None]
def _copy_internals(self, clone=_clone, **kw):
self.element = clone(self.element, **kw)
if self.order_by is not None:
self.order_by = clone(self.order_by, **kw)
@property
def _from_objects(self):
return list(
itertools.chain(
*[
c._from_objects
for c in (self.element, self.order_by)
if c is not None
]
)
)
class FunctionFilter(ColumnElement):
"""Represent a function FILTER clause.
This is a special operator against aggregate and window functions,
which controls which rows are passed to it.
It's supported only by certain database backends.
Invocation of :class:`.FunctionFilter` is via
:meth:`.FunctionElement.filter`::
func.count(1).filter(True)
.. versionadded:: 1.0.0
.. seealso::
:meth:`.FunctionElement.filter`
"""
__visit_name__ = "funcfilter"
criterion = None
def __init__(self, func, *criterion):
"""Produce a :class:`.FunctionFilter` object against a function.
Used against aggregate and window functions,
for database backends that support the "FILTER" clause.
E.g.::
from sqlalchemy import funcfilter
funcfilter(func.count(1), MyClass.name == 'some name')
Would produce "COUNT(1) FILTER (WHERE myclass.name = 'some name')".
This function is also available from the :data:`~.expression.func`
construct itself via the :meth:`.FunctionElement.filter` method.
.. versionadded:: 1.0.0
.. seealso::
:meth:`.FunctionElement.filter`
"""
self.func = func
self.filter(*criterion)
def filter(self, *criterion):
"""Produce an additional FILTER against the function.
This method adds additional criteria to the initial criteria
set up by :meth:`.FunctionElement.filter`.
Multiple criteria are joined together at SQL render time
via ``AND``.
"""
for criterion in list(criterion):
criterion = _expression_literal_as_text(criterion)
if self.criterion is not None:
self.criterion = self.criterion & criterion
else:
self.criterion = criterion
return self
def over(self, partition_by=None, order_by=None, range_=None, rows=None):
"""Produce an OVER clause against this filtered function.
Used against aggregate or so-called "window" functions,
for database backends that support window functions.
The expression::
func.rank().filter(MyClass.y > 5).over(order_by='x')
is shorthand for::
from sqlalchemy import over, funcfilter
over(funcfilter(func.rank(), MyClass.y > 5), order_by='x')
See :func:`_expression.over` for a full description.
"""
return Over(
self,
partition_by=partition_by,
order_by=order_by,
range_=range_,
rows=rows,
)
def self_group(self, against=None):
if operators.is_precedent(operators.filter_op, against):
return Grouping(self)
else:
return self
@util.memoized_property
def type(self):
return self.func.type
def get_children(self, **kwargs):
return [c for c in (self.func, self.criterion) if c is not None]
def _copy_internals(self, clone=_clone, **kw):
self.func = clone(self.func, **kw)
if self.criterion is not None:
self.criterion = clone(self.criterion, **kw)
@property
def _from_objects(self):
return list(
itertools.chain(
*[
c._from_objects
for c in (self.func, self.criterion)
if c is not None
]
)
)
class Label(ColumnElement):
"""Represents a column label (AS).
Represent a label, as typically applied to any column-level
element using the ``AS`` sql keyword.
"""
__visit_name__ = "label"
def __init__(self, name, element, type_=None):
"""Return a :class:`Label` object for the
given :class:`_expression.ColumnElement`.
A label changes the name of an element in the columns clause of a
``SELECT`` statement, typically via the ``AS`` SQL keyword.
This functionality is more conveniently available via the
:meth:`_expression.ColumnElement.label` method on
:class:`_expression.ColumnElement`.
:param name: label name
:param obj: a :class:`_expression.ColumnElement`.
"""
if isinstance(element, Label):
self._resolve_label = element._label
while isinstance(element, Label):
element = element.element
if name:
self.name = name
self._resolve_label = self.name
else:
self.name = _anonymous_label(
"%%(%d %s)s" % (id(self), getattr(element, "name", "anon"))
)
self.key = self._label = self._key_label = self.name
self._element = element
self._type = type_
self._proxies = [element]
def __reduce__(self):
return self.__class__, (self.name, self._element, self._type)
@util.memoized_property
def _is_implicitly_boolean(self):
return self.element._is_implicitly_boolean
@util.memoized_property
def _allow_label_resolve(self):
return self.element._allow_label_resolve
@property
def _order_by_label_element(self):
return self
@util.memoized_property
def type(self):
return type_api.to_instance(
self._type or getattr(self._element, "type", None)
)
@util.memoized_property
def element(self):
return self._element.self_group(against=operators.as_)
def self_group(self, against=None):
return self._apply_to_inner(self._element.self_group, against=against)
def _negate(self):
return self._apply_to_inner(self._element._negate)
def _apply_to_inner(self, fn, *arg, **kw):
sub_element = fn(*arg, **kw)
if sub_element is not self._element:
return Label(self.name, sub_element, type_=self._type)
else:
return self
@property
def primary_key(self):
return self.element.primary_key
@property
def foreign_keys(self):
return self.element.foreign_keys
def get_children(self, **kwargs):
return (self.element,)
def _copy_internals(self, clone=_clone, anonymize_labels=False, **kw):
self._element = clone(self._element, **kw)
self.__dict__.pop("element", None)
self.__dict__.pop("_allow_label_resolve", None)
if anonymize_labels:
self.name = self._resolve_label = _anonymous_label(
"%%(%d %s)s"
% (id(self), getattr(self.element, "name", "anon"))
)
self.key = self._label = self._key_label = self.name
@property
def _from_objects(self):
return self.element._from_objects
def _make_proxy(self, selectable, name=None, **kw):
e = self.element._make_proxy(
selectable,
name=name if name else self.name,
disallow_is_literal=True,
)
e._proxies.append(self)
if self._type is not None:
e.type = self._type
return e
class ColumnClause(Immutable, ColumnElement):
"""Represents a column expression from any textual string.
The :class:`.ColumnClause`, a lightweight analogue to the
:class:`_schema.Column` class, is typically invoked using the
:func:`_expression.column` function, as in::
from sqlalchemy import column
id, name = column("id"), column("name")
stmt = select([id, name]).select_from("user")
The above statement would produce SQL like::
SELECT id, name FROM user
:class:`.ColumnClause` is the immediate superclass of the schema-specific
:class:`_schema.Column` object. While the :class:`_schema.Column`
class has all the
same capabilities as :class:`.ColumnClause`, the :class:`.ColumnClause`
class is usable by itself in those cases where behavioral requirements
are limited to simple SQL expression generation. The object has none of
the associations with schema-level metadata or with execution-time
behavior that :class:`_schema.Column` does,
so in that sense is a "lightweight"
version of :class:`_schema.Column`.
Full details on :class:`.ColumnClause` usage is at
:func:`_expression.column`.
.. seealso::
:func:`_expression.column`
:class:`_schema.Column`
"""
__visit_name__ = "column"
onupdate = default = server_default = server_onupdate = None
_is_multiparam_column = False
_memoized_property = util.group_expirable_memoized_property()
def __init__(self, text, type_=None, is_literal=False, _selectable=None):
"""Produce a :class:`.ColumnClause` object.
The :class:`.ColumnClause` is a lightweight analogue to the
:class:`_schema.Column` class. The :func:`_expression.column`
function can
be invoked with just a name alone, as in::
from sqlalchemy import column
id, name = column("id"), column("name")
stmt = select([id, name]).select_from("user")
The above statement would produce SQL like::
SELECT id, name FROM user
Once constructed, :func:`_expression.column`
may be used like any other SQL
expression element such as within :func:`_expression.select`
constructs::
from sqlalchemy.sql import column
id, name = column("id"), column("name")
stmt = select([id, name]).select_from("user")
The text handled by :func:`_expression.column`
is assumed to be handled
like the name of a database column; if the string contains mixed case,
special characters, or matches a known reserved word on the target
backend, the column expression will render using the quoting
behavior determined by the backend. To produce a textual SQL
expression that is rendered exactly without any quoting,
use :func:`_expression.literal_column` instead,
or pass ``True`` as the
value of :paramref:`_expression.column.is_literal`. Additionally,
full SQL
statements are best handled using the :func:`_expression.text`
construct.
:func:`_expression.column` can be used in a table-like
fashion by combining it with the :func:`.table` function
(which is the lightweight analogue to :class:`_schema.Table`
) to produce
a working table construct with minimal boilerplate::
from sqlalchemy import table, column, select
user = table("user",
column("id"),
column("name"),
column("description"),
)
stmt = select([user.c.description]).where(user.c.name == 'wendy')
A :func:`_expression.column` / :func:`.table`
construct like that illustrated
above can be created in an
ad-hoc fashion and is not associated with any
:class:`_schema.MetaData`, DDL, or events, unlike its
:class:`_schema.Table` counterpart.
.. versionchanged:: 1.0.0 :func:`_expression.column` can now
be imported from the plain ``sqlalchemy`` namespace like any
other SQL element.
:param text: the text of the element.
:param type: :class:`_types.TypeEngine` object which can associate
this :class:`.ColumnClause` with a type.
:param is_literal: if True, the :class:`.ColumnClause` is assumed to
be an exact expression that will be delivered to the output with no
quoting rules applied regardless of case sensitive settings. the
:func:`_expression.literal_column()` function essentially invokes
:func:`_expression.column` while passing ``is_literal=True``.
.. seealso::
:class:`_schema.Column`
:func:`_expression.literal_column`
:func:`.table`
:func:`_expression.text`
:ref:`sqlexpression_literal_column`
"""
self.key = self.name = text
self.table = _selectable
self.type = type_api.to_instance(type_)
self.is_literal = is_literal
def _compare_name_for_result(self, other):
if (
self.is_literal
or self.table is None
or self.table._textual
or not hasattr(other, "proxy_set")
or (
isinstance(other, ColumnClause)
and (
other.is_literal
or other.table is None
or other.table._textual
)
)
):
return (hasattr(other, "name") and self.name == other.name) or (
hasattr(other, "_label") and self._label == other._label
)
else:
return other.proxy_set.intersection(self.proxy_set)
def _get_table(self):
return self.__dict__["table"]
def _set_table(self, table):
self._memoized_property.expire_instance(self)
self.__dict__["table"] = table
table = property(_get_table, _set_table)
@_memoized_property
def _from_objects(self):
t = self.table
if t is not None:
return [t]
else:
return []
@util.memoized_property
def description(self):
if util.py3k:
return self.name
else:
return self.name.encode("ascii", "backslashreplace")
@_memoized_property
def _key_label(self):
if self.key != self.name:
return self._gen_label(self.key)
else:
return self._label
@_memoized_property
def _label(self):
return self._gen_label(self.name)
@_memoized_property
def _render_label_in_columns_clause(self):
return self.table is not None
@property
def _ddl_label(self):
return self._gen_label(self.name, dedupe_on_key=False)
def _gen_label(self, name, dedupe_on_key=True):
t = self.table
if self.is_literal:
return None
elif t is not None and t.named_with_column:
if getattr(t, "schema", None):
label = t.schema.replace(".", "_") + "_" + t.name + "_" + name
else:
label = t.name + "_" + name
# propagate name quoting rules for labels.
if getattr(name, "quote", None) is not None:
if isinstance(label, quoted_name):
label.quote = name.quote
else:
label = quoted_name(label, name.quote)
elif getattr(t.name, "quote", None) is not None:
# can't get this situation to occur, so let's
# assert false on it for now
assert not isinstance(label, quoted_name)
label = quoted_name(label, t.name.quote)
if dedupe_on_key:
# ensure the label name doesn't conflict with that of an
# existing column. note that this implies that any Column
# must **not** set up its _label before its parent table has
# all of its other Column objects set up. There are several
# tables in the test suite which will fail otherwise; example:
# table "owner" has columns "name" and "owner_name". Therefore
# column owner.name cannot use the label "owner_name", it has
# to be "owner_name_1".
if label in t.c:
_label = label
counter = 1
while _label in t.c:
_label = label + "_" + str(counter)
counter += 1
label = _label
return _as_truncated(label)
else:
return name
def _bind_param(self, operator, obj, type_=None):
return BindParameter(
self.key,
obj,
_compared_to_operator=operator,
_compared_to_type=self.type,
type_=type_,
unique=True,
)
def _make_proxy(
self,
selectable,
name=None,
attach=True,
name_is_truncatable=False,
disallow_is_literal=False,
**kw
):
# the "is_literal" flag normally should never be propagated; a proxied
# column is always a SQL identifier and never the actual expression
# being evaluated. however, there is a case where the "is_literal" flag
# might be used to allow the given identifier to have a fixed quoting
# pattern already, so maintain the flag for the proxy unless a
# :class:`.Label` object is creating the proxy. See [ticket:4730].
is_literal = (
not disallow_is_literal
and self.is_literal
and (
# note this does not accommodate for quoted_name differences
# right now
name is None
or name == self.name
)
)
c = self._constructor(
_as_truncated(name or self.name)
if name_is_truncatable
else (name or self.name),
type_=self.type,
_selectable=selectable,
is_literal=is_literal,
)
if name is None:
c.key = self.key
c._proxies = [self]
if selectable._is_clone_of is not None:
c._is_clone_of = selectable._is_clone_of.columns.get(c.key)
if attach:
selectable._columns[c.key] = c
return c
class CollationClause(ColumnElement):
__visit_name__ = "collation"
def __init__(self, collation):
self.collation = collation
class _IdentifiedClause(Executable, ClauseElement):
__visit_name__ = "identified"
_execution_options = Executable._execution_options.union(
{"autocommit": False}
)
def __init__(self, ident):
self.ident = ident
class SavepointClause(_IdentifiedClause):
__visit_name__ = "savepoint"
class RollbackToSavepointClause(_IdentifiedClause):
__visit_name__ = "rollback_to_savepoint"
class ReleaseSavepointClause(_IdentifiedClause):
__visit_name__ = "release_savepoint"
class quoted_name(util.MemoizedSlots, util.text_type):
"""Represent a SQL identifier combined with quoting preferences.
:class:`.quoted_name` is a Python unicode/str subclass which
represents a particular identifier name along with a
``quote`` flag. This ``quote`` flag, when set to
``True`` or ``False``, overrides automatic quoting behavior
for this identifier in order to either unconditionally quote
or to not quote the name. If left at its default of ``None``,
quoting behavior is applied to the identifier on a per-backend basis
based on an examination of the token itself.
A :class:`.quoted_name` object with ``quote=True`` is also
prevented from being modified in the case of a so-called
"name normalize" option. Certain database backends, such as
Oracle, Firebird, and DB2 "normalize" case-insensitive names
as uppercase. The SQLAlchemy dialects for these backends
convert from SQLAlchemy's lower-case-means-insensitive convention
to the upper-case-means-insensitive conventions of those backends.
The ``quote=True`` flag here will prevent this conversion from occurring
to support an identifier that's quoted as all lower case against
such a backend.
The :class:`.quoted_name` object is normally created automatically
when specifying the name for key schema constructs such as
:class:`_schema.Table`, :class:`_schema.Column`, and others.
The class can also be
passed explicitly as the name to any function that receives a name which
can be quoted. Such as to use the :meth:`_engine.Engine.has_table`
method with
an unconditionally quoted name::
from sqlalchemy import create_engine
from sqlalchemy.sql import quoted_name
engine = create_engine("oracle+cx_oracle://some_dsn")
engine.has_table(quoted_name("some_table", True))
The above logic will run the "has table" logic against the Oracle backend,
passing the name exactly as ``"some_table"`` without converting to
upper case.
.. versionadded:: 0.9.0
.. versionchanged:: 1.2 The :class:`.quoted_name` construct is now
importable from ``sqlalchemy.sql``, in addition to the previous
location of ``sqlalchemy.sql.elements``.
"""
__slots__ = "quote", "lower", "upper"
def __new__(cls, value, quote):
if value is None:
return None
# experimental - don't bother with quoted_name
# if quote flag is None. doesn't seem to make any dent
# in performance however
# elif not sprcls and quote is None:
# return value
elif isinstance(value, cls) and (
quote is None or value.quote == quote
):
return value
self = super(quoted_name, cls).__new__(cls, value)
self.quote = quote
return self
def __reduce__(self):
return quoted_name, (util.text_type(self), self.quote)
def _memoized_method_lower(self):
if self.quote:
return self
else:
return util.text_type(self).lower()
def _memoized_method_upper(self):
if self.quote:
return self
else:
return util.text_type(self).upper()
def __repr__(self):
if util.py2k:
backslashed = self.encode("ascii", "backslashreplace")
if not util.py2k:
backslashed = backslashed.decode("ascii")
return "'%s'" % backslashed
else:
return str.__repr__(self)
class _truncated_label(quoted_name):
"""A unicode subclass used to identify symbolic "
"names that may require truncation."""
__slots__ = ()
def __new__(cls, value, quote=None):
quote = getattr(value, "quote", quote)
# return super(_truncated_label, cls).__new__(cls, value, quote, True)
return super(_truncated_label, cls).__new__(cls, value, quote)
def __reduce__(self):
return self.__class__, (util.text_type(self), self.quote)
def apply_map(self, map_):
return self
class conv(_truncated_label):
"""Mark a string indicating that a name has already been converted
by a naming convention.
This is a string subclass that indicates a name that should not be
subject to any further naming conventions.
E.g. when we create a :class:`.Constraint` using a naming convention
as follows::
m = MetaData(naming_convention={
"ck": "ck_%(table_name)s_%(constraint_name)s"
})
t = Table('t', m, Column('x', Integer),
CheckConstraint('x > 5', name='x5'))
The name of the above constraint will be rendered as ``"ck_t_x5"``.
That is, the existing name ``x5`` is used in the naming convention as the
``constraint_name`` token.
In some situations, such as in migration scripts, we may be rendering
the above :class:`.CheckConstraint` with a name that's already been
converted. In order to make sure the name isn't double-modified, the
new name is applied using the :func:`_schema.conv` marker. We can
use this explicitly as follows::
m = MetaData(naming_convention={
"ck": "ck_%(table_name)s_%(constraint_name)s"
})
t = Table('t', m, Column('x', Integer),
CheckConstraint('x > 5', name=conv('ck_t_x5')))
Where above, the :func:`_schema.conv` marker indicates that the constraint
name here is final, and the name will render as ``"ck_t_x5"`` and not
``"ck_t_ck_t_x5"``
.. versionadded:: 0.9.4
.. seealso::
:ref:`constraint_naming_conventions`
"""
__slots__ = ()
class _defer_name(_truncated_label):
"""mark a name as 'deferred' for the purposes of automated name
generation.
"""
__slots__ = ()
def __new__(cls, value):
if value is None:
return _NONE_NAME
elif isinstance(value, conv):
return value
else:
return super(_defer_name, cls).__new__(cls, value)
def __reduce__(self):
return self.__class__, (util.text_type(self),)
class _defer_none_name(_defer_name):
"""indicate a 'deferred' name that was ultimately the value None."""
__slots__ = ()
_NONE_NAME = _defer_none_name("_unnamed_")
# for backwards compatibility in case
# someone is re-implementing the
# _truncated_identifier() sequence in a custom
# compiler
_generated_label = _truncated_label
class _anonymous_label(_truncated_label):
"""A unicode subclass used to identify anonymously
generated names."""
__slots__ = ()
def __add__(self, other):
return _anonymous_label(
quoted_name(
util.text_type.__add__(self, util.text_type(other)), self.quote
)
)
def __radd__(self, other):
return _anonymous_label(
quoted_name(
util.text_type.__add__(util.text_type(other), self), self.quote
)
)
def apply_map(self, map_):
if self.quote is not None:
# preserve quoting only if necessary
return quoted_name(self % map_, self.quote)
else:
# else skip the constructor call
return self % map_
def _as_truncated(value):
"""coerce the given value to :class:`._truncated_label`.
Existing :class:`._truncated_label` and
:class:`._anonymous_label` objects are passed
unchanged.
"""
if isinstance(value, _truncated_label):
return value
else:
return _truncated_label(value)
def _string_or_unprintable(element):
if isinstance(element, util.string_types):
return element
else:
try:
return str(element)
except Exception:
return "unprintable element %r" % element
def _expand_cloned(elements):
"""expand the given set of ClauseElements to be the set of all 'cloned'
predecessors.
"""
return itertools.chain(*[x._cloned_set for x in elements])
def _select_iterables(elements):
"""expand tables into individual columns in the
given list of column expressions.
"""
return itertools.chain(*[c._select_iterable for c in elements])
def _cloned_intersection(a, b):
"""return the intersection of sets a and b, counting
any overlap between 'cloned' predecessors.
The returned set is in terms of the entities present within 'a'.
"""
all_overlap = set(_expand_cloned(a)).intersection(_expand_cloned(b))
return set(
elem for elem in a if all_overlap.intersection(elem._cloned_set)
)
def _cloned_difference(a, b):
all_overlap = set(_expand_cloned(a)).intersection(_expand_cloned(b))
return set(
elem for elem in a if not all_overlap.intersection(elem._cloned_set)
)
@util.dependencies("sqlalchemy.sql.functions")
def _labeled(functions, element):
if not hasattr(element, "name") or isinstance(
element, functions.FunctionElement
):
return element.label(None)
else:
return element
def _is_column(col):
"""True if ``col`` is an instance of
:class:`_expression.ColumnElement`. """
return isinstance(col, ColumnElement)
def _find_columns(clause):
"""locate Column objects within the given expression."""
cols = util.column_set()
traverse(clause, {}, {"column": cols.add})
return cols
# there is some inconsistency here between the usage of
# inspect() vs. checking for Visitable and __clause_element__.
# Ideally all functions here would derive from inspect(),
# however the inspect() versions add significant callcount
# overhead for critical functions like _interpret_as_column_or_from().
# Generally, the column-based functions are more performance critical
# and are fine just checking for __clause_element__(). It is only
# _interpret_as_from() where we'd like to be able to receive ORM entities
# that have no defined namespace, hence inspect() is needed there.
def _column_as_key(element):
if isinstance(element, util.string_types):
return element
if hasattr(element, "__clause_element__"):
element = element.__clause_element__()
try:
return element.key
except AttributeError:
return None
def _clause_element_as_expr(element):
if hasattr(element, "__clause_element__"):
return element.__clause_element__()
else:
return element
def _literal_as_label_reference(element):
if isinstance(element, util.string_types):
return _textual_label_reference(element)
elif hasattr(element, "__clause_element__"):
element = element.__clause_element__()
return _literal_as_text(element)
def _literal_and_labels_as_label_reference(element):
if isinstance(element, util.string_types):
return _textual_label_reference(element)
elif hasattr(element, "__clause_element__"):
element = element.__clause_element__()
if (
isinstance(element, ColumnElement)
and element._order_by_label_element is not None
):
return _label_reference(element)
else:
return _literal_as_text(element)
def _expression_literal_as_text(element):
return _literal_as_text(element)
def _literal_as(element, text_fallback):
if isinstance(element, Visitable):
return element
elif hasattr(element, "__clause_element__"):
return element.__clause_element__()
elif isinstance(element, util.string_types):
return text_fallback(element)
elif isinstance(element, (util.NoneType, bool)):
return _const_expr(element)
else:
raise exc.ArgumentError(
"SQL expression object expected, got object of type %r "
"instead" % type(element)
)
def _literal_as_text(element, allow_coercion_to_text=False):
if allow_coercion_to_text:
return _literal_as(element, TextClause)
else:
return _literal_as(element, _no_text_coercion)
def _literal_as_column(element):
return _literal_as(element, ColumnClause)
def _no_column_coercion(element):
element = str(element)
guess_is_literal = not _guess_straight_column.match(element)
raise exc.ArgumentError(
"Textual column expression %(column)r should be "
"explicitly declared with text(%(column)r), "
"or use %(literal_column)s(%(column)r) "
"for more specificity"
% {
"column": util.ellipses_string(element),
"literal_column": "literal_column"
if guess_is_literal
else "column",
}
)
def _no_text_coercion(
element, exc_cls=exc.ArgumentError, extra=None, err=None
):
util.raise_(
exc_cls(
"%(extra)sTextual SQL expression %(expr)r should be "
"explicitly declared as text(%(expr)r)"
% {
"expr": util.ellipses_string(element),
"extra": "%s " % extra if extra else "",
}
),
replace_context=err,
)
def _no_literals(element):
if hasattr(element, "__clause_element__"):
return element.__clause_element__()
elif not isinstance(element, Visitable):
raise exc.ArgumentError(
"Ambiguous literal: %r. Use the 'text()' "
"function to indicate a SQL expression "
"literal, or 'literal()' to indicate a "
"bound value." % (element,)
)
else:
return element
def _is_literal(element):
return not isinstance(element, Visitable) and not hasattr(
element, "__clause_element__"
)
def _only_column_elements_or_none(element, name):
if element is None:
return None
else:
return _only_column_elements(element, name)
def _only_column_elements(element, name):
if hasattr(element, "__clause_element__"):
element = element.__clause_element__()
if not isinstance(element, ColumnElement):
raise exc.ArgumentError(
"Column-based expression object expected for argument "
"'%s'; got: '%s', type %s" % (name, element, type(element))
)
return element
def _literal_as_binds(element, name=None, type_=None):
if hasattr(element, "__clause_element__"):
return element.__clause_element__()
elif not isinstance(element, Visitable):
if element is None:
return Null()
else:
return BindParameter(name, element, type_=type_, unique=True)
else:
return element
_guess_straight_column = re.compile(r"^\w\S*$", re.I)
def _interpret_as_column_or_from(element):
if isinstance(element, Visitable):
return element
elif hasattr(element, "__clause_element__"):
return element.__clause_element__()
insp = inspection.inspect(element, raiseerr=False)
if insp is None:
if isinstance(element, (util.NoneType, bool)):
return _const_expr(element)
elif hasattr(insp, "selectable"):
return insp.selectable
# be forgiving as this is an extremely common
# and known expression
if element == "*":
guess_is_literal = True
elif isinstance(element, (numbers.Number)):
return ColumnClause(str(element), is_literal=True)
else:
_no_column_coercion(element)
return ColumnClause(element, is_literal=guess_is_literal)
def _const_expr(element):
if isinstance(element, (Null, False_, True_)):
return element
elif element is None:
return Null()
elif element is False:
return False_()
elif element is True:
return True_()
else:
raise exc.ArgumentError("Expected None, False, or True")
def _type_from_args(args):
for a in args:
if not a.type._isnull:
return a.type
else:
return type_api.NULLTYPE
def _corresponding_column_or_error(fromclause, column, require_embedded=False):
c = fromclause.corresponding_column(
column, require_embedded=require_embedded
)
if c is None:
raise exc.InvalidRequestError(
"Given column '%s', attached to table '%s', "
"failed to locate a corresponding column from table '%s'"
% (column, getattr(column, "table", None), fromclause.description)
)
return c
class AnnotatedColumnElement(Annotated):
def __init__(self, element, values):
Annotated.__init__(self, element, values)
ColumnElement.comparator._reset(self)
for attr in ("name", "key", "table"):
if self.__dict__.get(attr, False) is None:
self.__dict__.pop(attr)
def _with_annotations(self, values):
clone = super(AnnotatedColumnElement, self)._with_annotations(values)
ColumnElement.comparator._reset(clone)
return clone
@util.memoized_property
def name(self):
"""pull 'name' from parent, if not present"""
return self._Annotated__element.name
@util.memoized_property
def table(self):
"""pull 'table' from parent, if not present"""
return self._Annotated__element.table
@util.memoized_property
def key(self):
"""pull 'key' from parent, if not present"""
return self._Annotated__element.key
@util.memoized_property
def info(self):
return self._Annotated__element.info
@util.memoized_property
def anon_label(self):
return self._Annotated__element.anon_label