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# orm/properties.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
"""MapperProperty implementations.
This is a private module which defines the behavior of individual ORM-
mapped attributes.
"""
from __future__ import absolute_import
from . import attributes
from .interfaces import PropComparator
from .interfaces import StrategizedProperty
from .util import _orm_full_deannotate
from .. import log
from .. import util
from ..sql import expression
__all__ = ["ColumnProperty"]
@log.class_logger
class ColumnProperty(StrategizedProperty):
"""Describes an object attribute that corresponds to a table column.
Public constructor is the :func:`_orm.column_property` function.
"""
strategy_wildcard_key = "column"
__slots__ = (
"_orig_columns",
"columns",
"group",
"deferred",
"instrument",
"comparator_factory",
"descriptor",
"extension",
"active_history",
"expire_on_flush",
"info",
"doc",
"strategy_key",
"_creation_order",
"_is_polymorphic_discriminator",
"_mapped_by_synonym",
"_deferred_column_loader",
)
@util.deprecated_params(
extension=(
"0.7",
":class:`.AttributeExtension` is deprecated in favor of the "
":class:`.AttributeEvents` listener interface. The "
":paramref:`.column_property.extension` parameter will be "
"removed in a future release.",
)
)
def __init__(self, *columns, **kwargs):
r"""Provide a column-level property for use with a mapping.
Column-based properties can normally be applied to the mapper's
``properties`` dictionary using the :class:`_schema.Column`
element directly.
Use this function when the given column is not directly present within
the mapper's selectable; examples include SQL expressions, functions,
and scalar SELECT queries.
The :func:`_orm.column_property` function returns an instance of
:class:`.ColumnProperty`.
Columns that aren't present in the mapper's selectable won't be
persisted by the mapper and are effectively "read-only" attributes.
:param \*cols:
list of Column objects to be mapped.
:param active_history=False:
When ``True``, indicates that the "previous" value for a
scalar attribute should be loaded when replaced, if not
already loaded. Normally, history tracking logic for
simple non-primary-key scalar values only needs to be
aware of the "new" value in order to perform a flush. This
flag is available for applications that make use of
:func:`.attributes.get_history` or :meth:`.Session.is_modified`
which also need to know
the "previous" value of the attribute.
:param comparator_factory: a class which extends
:class:`.ColumnProperty.Comparator` which provides custom SQL
clause generation for comparison operations.
:param group:
a group name for this property when marked as deferred.
:param deferred:
when True, the column property is "deferred", meaning that
it does not load immediately, and is instead loaded when the
attribute is first accessed on an instance. See also
:func:`~sqlalchemy.orm.deferred`.
:param doc:
optional string that will be applied as the doc on the
class-bound descriptor.
:param expire_on_flush=True:
Disable expiry on flush. A column_property() which refers
to a SQL expression (and not a single table-bound column)
is considered to be a "read only" property; populating it
has no effect on the state of data, and it can only return
database state. For this reason a column_property()'s value
is expired whenever the parent object is involved in a
flush, that is, has any kind of "dirty" state within a flush.
Setting this parameter to ``False`` will have the effect of
leaving any existing value present after the flush proceeds.
Note however that the :class:`.Session` with default expiration
settings still expires
all attributes after a :meth:`.Session.commit` call, however.
:param info: Optional data dictionary which will be populated into the
:attr:`.MapperProperty.info` attribute of this object.
:param extension:
an :class:`.AttributeExtension` instance, or list of extensions,
which will be prepended to the list of attribute listeners for the
resulting descriptor placed on the class.
.. seealso::
:ref:`column_property_options` - to map columns while including
mapping options
:ref:`mapper_column_property_sql_expressions` - to map SQL
expressions
"""
super(ColumnProperty, self).__init__()
self._orig_columns = [expression._labeled(c) for c in columns]
self.columns = [
expression._labeled(_orm_full_deannotate(c)) for c in columns
]
self.group = kwargs.pop("group", None)
self.deferred = kwargs.pop("deferred", False)
self.instrument = kwargs.pop("_instrument", True)
self.comparator_factory = kwargs.pop(
"comparator_factory", self.__class__.Comparator
)
self.descriptor = kwargs.pop("descriptor", None)
self.extension = kwargs.pop("extension", None)
self.active_history = kwargs.pop("active_history", False)
self.expire_on_flush = kwargs.pop("expire_on_flush", True)
if "info" in kwargs:
self.info = kwargs.pop("info")
if "doc" in kwargs:
self.doc = kwargs.pop("doc")
else:
for col in reversed(self.columns):
doc = getattr(col, "doc", None)
if doc is not None:
self.doc = doc
break
else:
self.doc = None
if kwargs:
raise TypeError(
"%s received unexpected keyword argument(s): %s"
% (self.__class__.__name__, ", ".join(sorted(kwargs.keys())))
)
util.set_creation_order(self)
self.strategy_key = (
("deferred", self.deferred),
("instrument", self.instrument),
)
@util.dependencies("sqlalchemy.orm.state", "sqlalchemy.orm.strategies")
def _memoized_attr__deferred_column_loader(self, state, strategies):
return state.InstanceState._instance_level_callable_processor(
self.parent.class_manager,
strategies.LoadDeferredColumns(self.key),
self.key,
)
def __clause_element__(self):
"""Allow the ColumnProperty to work in expression before it is turned
into an instrumented attribute.
"""
return self.expression
@property
def expression(self):
"""Return the primary column or expression for this ColumnProperty.
E.g.::
class File(Base):
# ...
name = Column(String(64))
extension = Column(String(8))
filename = column_property(name + '.' + extension)
path = column_property('C:/' + filename.expression)
.. seealso::
:ref:`mapper_column_property_sql_expressions_composed`
"""
return self.columns[0]
def instrument_class(self, mapper):
if not self.instrument:
return
attributes.register_descriptor(
mapper.class_,
self.key,
comparator=self.comparator_factory(self, mapper),
parententity=mapper,
doc=self.doc,
)
def do_init(self):
super(ColumnProperty, self).do_init()
if len(self.columns) > 1 and set(self.parent.primary_key).issuperset(
self.columns
):
util.warn(
(
"On mapper %s, primary key column '%s' is being combined "
"with distinct primary key column '%s' in attribute '%s'. "
"Use explicit properties to give each column its own "
"mapped attribute name."
)
% (self.parent, self.columns[1], self.columns[0], self.key)
)
def copy(self):
return ColumnProperty(
deferred=self.deferred,
group=self.group,
active_history=self.active_history,
*self.columns
)
def _getcommitted(
self, state, dict_, column, passive=attributes.PASSIVE_OFF
):
return state.get_impl(self.key).get_committed_value(
state, dict_, passive=passive
)
def merge(
self,
session,
source_state,
source_dict,
dest_state,
dest_dict,
load,
_recursive,
_resolve_conflict_map,
):
if not self.instrument:
return
elif self.key in source_dict:
value = source_dict[self.key]
if not load:
dest_dict[self.key] = value
else:
impl = dest_state.get_impl(self.key)
impl.set(dest_state, dest_dict, value, None)
elif dest_state.has_identity and self.key not in dest_dict:
dest_state._expire_attributes(
dest_dict, [self.key], no_loader=True
)
class Comparator(util.MemoizedSlots, PropComparator):
"""Produce boolean, comparison, and other operators for
:class:`.ColumnProperty` attributes.
See the documentation for :class:`.PropComparator` for a brief
overview.
.. seealso::
:class:`.PropComparator`
:class:`.ColumnOperators`
:ref:`types_operators`
:attr:`.TypeEngine.comparator_factory`
"""
__slots__ = "__clause_element__", "info", "expressions"
def _memoized_method___clause_element__(self):
if self.adapter:
return self.adapter(self.prop.columns[0])
else:
# no adapter, so we aren't aliased
# assert self._parententity is self._parentmapper
return self.prop.columns[0]._annotate(
{
"parententity": self._parententity,
"parentmapper": self._parententity,
}
)
def _memoized_attr_info(self):
"""The .info dictionary for this attribute."""
ce = self.__clause_element__()
try:
return ce.info
except AttributeError:
return self.prop.info
def _memoized_attr_expressions(self):
"""The full sequence of columns referenced by this
attribute, adjusted for any aliasing in progress.
.. versionadded:: 1.3.17
"""
if self.adapter:
return [self.adapter(col) for col in self.prop.columns]
else:
# no adapter, so we aren't aliased
# assert self._parententity is self._parentmapper
return [
col._annotate(
{
"parententity": self._parententity,
"parentmapper": self._parententity,
"orm_key": self.prop.key,
}
)
for col in self.prop.columns
]
def _fallback_getattr(self, key):
"""proxy attribute access down to the mapped column.
this allows user-defined comparison methods to be accessed.
"""
return getattr(self.__clause_element__(), key)
def operate(self, op, *other, **kwargs):
return op(self.__clause_element__(), *other, **kwargs)
def reverse_operate(self, op, other, **kwargs):
col = self.__clause_element__()
return op(col._bind_param(op, other), col, **kwargs)
def __str__(self):
return str(self.parent.class_.__name__) + "." + self.key
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