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# sql/elements.py
# Copyright (C) 2005-2021 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 operator
import re
from . import coercions
from . import operators
from . import roles
from . import traversals
from . import type_api
from .annotation import Annotated
from .annotation import SupportsWrappingAnnotations
from .base import _clone
from .base import _generative
from .base import Executable
from .base import HasMemoized
from .base import Immutable
from .base import NO_ARG
from .base import PARSE_AUTOCOMMIT
from .base import SingletonConstant
from .coercions import _document_text_coercion
from .traversals import _get_children
from .traversals import HasCopyInternals
from .traversals import MemoizedHasCacheKey
from .traversals import NO_CACHE
from .visitors import cloned_traverse
from .visitors import InternalTraversal
from .visitors import traverse
from .visitors import Traversible
from .. import exc
from .. import inspection
from .. import util
if util.TYPE_CHECKING:
from typing import Any
from typing import Optional
from typing import Union
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 = coercions.expect(roles.ExpressionElementRole, 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 = coercions.expect(roles.ExpressionElementRole, 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 coercions.expect(roles.LiteralValueRole, value, type_=type_)
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.CursorResult` 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(coercions.expect(roles.ExpressionElementRole, clause))
@inspection._self_inspects
class ClauseElement(
roles.SQLRole,
SupportsWrappingAnnotations,
MemoizedHasCacheKey,
HasCopyInternals,
Traversible,
):
"""Base class for elements of a programmatically constructed SQL
expression.
"""
__visit_name__ = "clause"
_propagate_attrs = util.immutabledict()
"""like annotations, however these propagate outwards liberally
as SQL constructs are built, and are set up at construction time.
"""
supports_execution = False
stringify_dialect = "default"
_from_objects = []
bind = None
description = None
_is_clone_of = None
is_clause_element = True
is_selectable = False
_is_textual = False
_is_from_clause = False
_is_returns_rows = False
_is_text_clause = False
_is_from_container = False
_is_select_container = False
_is_select_statement = False
_is_bind_parameter = False
_is_clause_list = False
_is_lambda_element = False
_order_by_label_element = None
_cache_key_traversal = None
def _set_propagate_attrs(self, values):
# usually, self._propagate_attrs is empty here. one case where it's
# not is a subquery against ORM select, that is then pulled as a
# property of an aliased class. should all be good
# assert not self._propagate_attrs
self._propagate_attrs = util.immutabledict(values)
return self
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.
"""
skip = self._memoized_keys
c = self.__class__.__new__(self.__class__)
c.__dict__ = {k: v for k, v in self.__dict__.items() if k not in skip}
# 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
def _with_binary_element_type(self, type_):
"""in the context of binary expression, convert the type of this
object to the one given.
applies only to :class:`_expression.ColumnElement` classes.
"""
return self
@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__
@HasMemoized.memoized_attribute
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)
d.pop("_generate_cache_key", None)
return d
def _execute_on_connection(
self, connection, multiparams, params, execution_options
):
if self.supports_execution:
return connection._execute_clauseelement(
self, multiparams, params, execution_options
)
else:
raise exc.ObjectNotExecutableError(self)
def unique_params(self, *optionaldict, **kwargs):
"""Return a copy with :func:`_expression.bindparam` elements
replaced.
Same functionality as :meth:`_expression.ClauseElement.params`,
except adds `unique=True`
to affected bind parameters so that multiple statements can be
used.
"""
return self._replace_params(True, optionaldict, kwargs)
def params(self, *optionaldict, **kwargs):
"""Return a copy with :func:`_expression.bindparam` elements
replaced.
Returns a copy of this ClauseElement with
:func:`_expression.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._replace_params(False, optionaldict, kwargs)
def _replace_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 :class:`_expression.ClauseElement` to
the given :class:`_expression.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 traversals.compare(self, other, **kw)
def get_children(self, omit_attrs=(), **kw):
r"""Return immediate child :class:`.visitors.Traversible`
elements of this :class:`.visitors.Traversible`.
This is used for visit traversal.
\**kw 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).
"""
try:
traverse_internals = self._traverse_internals
except AttributeError:
# user-defined classes may not have a _traverse_internals
return []
return itertools.chain.from_iterable(
meth(obj, **kw)
for attrname, obj, meth in _get_children.run_generated_dispatch(
self, traverse_internals, "_generated_get_children_traversal"
)
if attrname not in omit_attrs and obj is not None
)
def self_group(self, against=None):
# type: (Optional[Any]) -> ClauseElement
"""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
def _ungroup(self):
"""Return this :class:`_expression.ClauseElement` """
"""without any groupings."""
return self
@util.preload_module("sqlalchemy.engine.default")
@util.preload_module("sqlalchemy.engine.url")
def compile(self, 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 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
else:
if self.stringify_dialect == "default":
default = util.preloaded.engine_default
dialect = default.StrCompileDialect()
else:
url = util.preloaded.engine_url
dialect = url.URL.create(
self.stringify_dialect
).get_dialect()()
return self._compiler(dialect, **kw)
def _compile_w_cache(
self,
dialect,
compiled_cache=None,
column_keys=None,
for_executemany=False,
schema_translate_map=None,
**kw
):
if compiled_cache is not None:
elem_cache_key = self._generate_cache_key()
else:
elem_cache_key = None
if elem_cache_key:
cache_key, extracted_params = elem_cache_key
key = (
dialect,
cache_key,
tuple(column_keys),
bool(schema_translate_map),
for_executemany,
)
compiled_sql = compiled_cache.get(key)
if compiled_sql is None:
cache_hit = dialect.CACHE_MISS
compiled_sql = self._compiler(
dialect,
cache_key=elem_cache_key,
column_keys=column_keys,
for_executemany=for_executemany,
schema_translate_map=schema_translate_map,
**kw
)
compiled_cache[key] = compiled_sql
else:
cache_hit = dialect.CACHE_HIT
else:
extracted_params = None
compiled_sql = self._compiler(
dialect,
cache_key=elem_cache_key,
column_keys=column_keys,
for_executemany=for_executemany,
schema_translate_map=schema_translate_map,
**kw
)
cache_hit = (
dialect.CACHING_DISABLED
if compiled_cache is None
else dialect.NO_CACHE_KEY
)
return compiled_sql, extracted_params, cache_hit
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
def __invert__(self):
# undocumented element currently used by the ORM for
# relationship.contains()
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
)
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(
roles.ColumnArgumentOrKeyRole,
roles.StatementOptionRole,
roles.WhereHavingRole,
roles.BinaryElementRole,
roles.OrderByRole,
roles.ColumnsClauseRole,
roles.LimitOffsetRole,
roles.DMLColumnRole,
roles.DDLConstraintColumnRole,
roles.DDLExpressionRole,
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 an accessor 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` and sometimes a
:class:`_expression.SelectBase` expression.
It is used within the ORM to
convert from ORM-specific objects like mapped classes and
mapped attributes into Core expression objects.
* 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 :class:`_schema.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):
# type: (Optional[Any]) -> ClauseElement
if (
against in (operators.and_, operators.or_, operators._asbool)
and self.type._type_affinity is type_api.BOOLEANTYPE._type_affinity
):
return AsBoolean(self, operators.is_true, operators.is_false)
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.is_false, operators.is_true)
else:
return super(ColumnElement, self)._negate()
@util.memoized_property
def type(self):
return type_api.NULLTYPE
@HasMemoized.memoized_attribute
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, expanding=False):
return BindParameter(
None,
obj,
_compared_to_operator=operator,
type_=type_,
_compared_to_type=self.type,
unique=True,
expanding=expanding,
)
@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
)
@util.memoized_property
def _proxy_key(self):
if self._annotations and "proxy_key" in self._annotations:
return self._annotations["proxy_key"]
elif self.key:
return self.key
else:
try:
return str(self)
except exc.UnsupportedCompilationError:
return self.anon_label
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
key = self._proxy_key
else:
key = name
co = ColumnClause(
coercions.expect(roles.TruncatedLabelRole, name)
if name_is_truncatable
else name,
type_=getattr(self, "type", None),
_selectable=selectable,
)
co._propagate_attrs = selectable._propagate_attrs
co._proxies = [self]
if selectable._is_clone_of is not None:
co._is_clone_of = selectable._is_clone_of.columns.get(key)
return key, co
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)
def _anon_label(self, seed):
while self._is_clone_of is not None:
self = self._is_clone_of
# as of 1.4 anonymous label for ColumnElement uses hash(), not id(),
# as the identifier, because a column and its annotated version are
# the same thing in a SQL statement
if isinstance(seed, _anonymous_label):
return _anonymous_label.safe_construct(
hash(self), "", enclosing_label=seed
)
return _anonymous_label.safe_construct(hash(self), seed or "anon")
@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.
"""
name = getattr(self, "name", None)
return self._anon_label(name)
@util.memoized_property
def anon_key_label(self):
"""Provides a constant 'anonymous key label' for this ColumnElement.
Compare to ``anon_label``, except that the "key" of the column,
if available, is used to generate the label.