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979 lines
30 KiB
979 lines
30 KiB
# orm/interfaces.py
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# Copyright (C) 2005-2022 the SQLAlchemy authors and contributors
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# <see AUTHORS file>
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#
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# This module is part of SQLAlchemy and is released under
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# the MIT License: https://www.opensource.org/licenses/mit-license.php
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"""
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Contains various base classes used throughout the ORM.
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Defines some key base classes prominent within the internals.
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This module and the classes within are mostly private, though some attributes
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are exposed when inspecting mappings.
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"""
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from __future__ import absolute_import
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import collections
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from . import exc as orm_exc
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from . import path_registry
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from .base import _MappedAttribute # noqa
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from .base import EXT_CONTINUE
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from .base import EXT_SKIP
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from .base import EXT_STOP
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from .base import InspectionAttr # noqa
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from .base import InspectionAttrInfo # noqa
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from .base import MANYTOMANY
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from .base import MANYTOONE
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from .base import NOT_EXTENSION
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from .base import ONETOMANY
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from .. import inspect
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from .. import inspection
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from .. import util
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from ..sql import operators
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from ..sql import roles
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from ..sql import visitors
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from ..sql.base import ExecutableOption
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from ..sql.traversals import HasCacheKey
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__all__ = (
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"EXT_CONTINUE",
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"EXT_STOP",
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"EXT_SKIP",
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"ONETOMANY",
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"MANYTOMANY",
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"MANYTOONE",
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"NOT_EXTENSION",
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"LoaderStrategy",
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"MapperOption",
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"LoaderOption",
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"MapperProperty",
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"PropComparator",
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"StrategizedProperty",
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)
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class ORMStatementRole(roles.StatementRole):
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_role_name = (
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"Executable SQL or text() construct, including ORM " "aware objects"
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)
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class ORMColumnsClauseRole(roles.ColumnsClauseRole):
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_role_name = "ORM mapped entity, aliased entity, or Column expression"
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class ORMEntityColumnsClauseRole(ORMColumnsClauseRole):
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_role_name = "ORM mapped or aliased entity"
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class ORMFromClauseRole(roles.StrictFromClauseRole):
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_role_name = "ORM mapped entity, aliased entity, or FROM expression"
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@inspection._self_inspects
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class MapperProperty(
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HasCacheKey, _MappedAttribute, InspectionAttr, util.MemoizedSlots
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):
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"""Represent a particular class attribute mapped by :class:`_orm.Mapper`.
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The most common occurrences of :class:`.MapperProperty` are the
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mapped :class:`_schema.Column`, which is represented in a mapping as
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an instance of :class:`.ColumnProperty`,
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and a reference to another class produced by :func:`_orm.relationship`,
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represented in the mapping as an instance of
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:class:`.RelationshipProperty`.
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"""
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__slots__ = (
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"_configure_started",
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"_configure_finished",
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"parent",
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"key",
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"info",
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)
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_cache_key_traversal = [
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("parent", visitors.ExtendedInternalTraversal.dp_has_cache_key),
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("key", visitors.ExtendedInternalTraversal.dp_string),
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]
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cascade = frozenset()
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"""The set of 'cascade' attribute names.
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This collection is checked before the 'cascade_iterator' method is called.
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The collection typically only applies to a RelationshipProperty.
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"""
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is_property = True
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"""Part of the InspectionAttr interface; states this object is a
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mapper property.
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"""
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@property
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def _links_to_entity(self):
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"""True if this MapperProperty refers to a mapped entity.
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Should only be True for RelationshipProperty, False for all others.
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"""
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raise NotImplementedError()
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def _memoized_attr_info(self):
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"""Info dictionary associated with the object, allowing user-defined
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data to be associated with this :class:`.InspectionAttr`.
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The dictionary is generated when first accessed. Alternatively,
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it can be specified as a constructor argument to the
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:func:`.column_property`, :func:`_orm.relationship`, or
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:func:`.composite`
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functions.
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.. versionchanged:: 1.0.0 :attr:`.MapperProperty.info` is also
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available on extension types via the
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:attr:`.InspectionAttrInfo.info` attribute, so that it can apply
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to a wider variety of ORM and extension constructs.
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.. seealso::
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:attr:`.QueryableAttribute.info`
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:attr:`.SchemaItem.info`
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"""
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return {}
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def setup(self, context, query_entity, path, adapter, **kwargs):
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"""Called by Query for the purposes of constructing a SQL statement.
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Each MapperProperty associated with the target mapper processes the
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statement referenced by the query context, adding columns and/or
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criterion as appropriate.
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"""
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def create_row_processor(
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self, context, query_entity, path, mapper, result, adapter, populators
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):
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"""Produce row processing functions and append to the given
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set of populators lists.
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"""
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def cascade_iterator(
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self, type_, state, dict_, visited_states, halt_on=None
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):
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"""Iterate through instances related to the given instance for
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a particular 'cascade', starting with this MapperProperty.
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Return an iterator3-tuples (instance, mapper, state).
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Note that the 'cascade' collection on this MapperProperty is
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checked first for the given type before cascade_iterator is called.
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This method typically only applies to RelationshipProperty.
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"""
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return iter(())
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def set_parent(self, parent, init):
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"""Set the parent mapper that references this MapperProperty.
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This method is overridden by some subclasses to perform extra
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setup when the mapper is first known.
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"""
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self.parent = parent
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def instrument_class(self, mapper):
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"""Hook called by the Mapper to the property to initiate
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instrumentation of the class attribute managed by this
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MapperProperty.
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The MapperProperty here will typically call out to the
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attributes module to set up an InstrumentedAttribute.
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This step is the first of two steps to set up an InstrumentedAttribute,
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and is called early in the mapper setup process.
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The second step is typically the init_class_attribute step,
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called from StrategizedProperty via the post_instrument_class()
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hook. This step assigns additional state to the InstrumentedAttribute
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(specifically the "impl") which has been determined after the
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MapperProperty has determined what kind of persistence
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management it needs to do (e.g. scalar, object, collection, etc).
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"""
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def __init__(self):
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self._configure_started = False
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self._configure_finished = False
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def init(self):
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"""Called after all mappers are created to assemble
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relationships between mappers and perform other post-mapper-creation
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initialization steps.
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"""
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self._configure_started = True
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self.do_init()
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self._configure_finished = True
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@property
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def class_attribute(self):
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"""Return the class-bound descriptor corresponding to this
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:class:`.MapperProperty`.
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This is basically a ``getattr()`` call::
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return getattr(self.parent.class_, self.key)
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I.e. if this :class:`.MapperProperty` were named ``addresses``,
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and the class to which it is mapped is ``User``, this sequence
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is possible::
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>>> from sqlalchemy import inspect
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>>> mapper = inspect(User)
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>>> addresses_property = mapper.attrs.addresses
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>>> addresses_property.class_attribute is User.addresses
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True
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>>> User.addresses.property is addresses_property
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True
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"""
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return getattr(self.parent.class_, self.key)
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def do_init(self):
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"""Perform subclass-specific initialization post-mapper-creation
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steps.
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This is a template method called by the ``MapperProperty``
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object's init() method.
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"""
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def post_instrument_class(self, mapper):
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"""Perform instrumentation adjustments that need to occur
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after init() has completed.
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The given Mapper is the Mapper invoking the operation, which
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may not be the same Mapper as self.parent in an inheritance
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scenario; however, Mapper will always at least be a sub-mapper of
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self.parent.
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This method is typically used by StrategizedProperty, which delegates
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it to LoaderStrategy.init_class_attribute() to perform final setup
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on the class-bound InstrumentedAttribute.
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"""
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def merge(
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self,
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session,
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source_state,
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source_dict,
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dest_state,
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dest_dict,
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load,
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_recursive,
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_resolve_conflict_map,
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):
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"""Merge the attribute represented by this ``MapperProperty``
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from source to destination object.
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"""
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def __repr__(self):
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return "<%s at 0x%x; %s>" % (
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self.__class__.__name__,
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id(self),
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getattr(self, "key", "no key"),
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)
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@inspection._self_inspects
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class PropComparator(operators.ColumnOperators):
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r"""Defines SQL operators for :class:`.MapperProperty` objects.
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SQLAlchemy allows for operators to
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be redefined at both the Core and ORM level. :class:`.PropComparator`
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is the base class of operator redefinition for ORM-level operations,
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including those of :class:`.ColumnProperty`,
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:class:`.RelationshipProperty`, and :class:`.CompositeProperty`.
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.. note:: With the advent of Hybrid properties introduced in SQLAlchemy
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0.7, as well as Core-level operator redefinition in
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SQLAlchemy 0.8, the use case for user-defined :class:`.PropComparator`
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instances is extremely rare. See :ref:`hybrids_toplevel` as well
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as :ref:`types_operators`.
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User-defined subclasses of :class:`.PropComparator` may be created. The
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built-in Python comparison and math operator methods, such as
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:meth:`.operators.ColumnOperators.__eq__`,
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:meth:`.operators.ColumnOperators.__lt__`, and
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:meth:`.operators.ColumnOperators.__add__`, can be overridden to provide
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new operator behavior. The custom :class:`.PropComparator` is passed to
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the :class:`.MapperProperty` instance via the ``comparator_factory``
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argument. In each case,
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the appropriate subclass of :class:`.PropComparator` should be used::
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# definition of custom PropComparator subclasses
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from sqlalchemy.orm.properties import \
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ColumnProperty,\
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CompositeProperty,\
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RelationshipProperty
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class MyColumnComparator(ColumnProperty.Comparator):
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def __eq__(self, other):
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return self.__clause_element__() == other
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class MyRelationshipComparator(RelationshipProperty.Comparator):
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def any(self, expression):
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"define the 'any' operation"
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# ...
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class MyCompositeComparator(CompositeProperty.Comparator):
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def __gt__(self, other):
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"redefine the 'greater than' operation"
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return sql.and_(*[a>b for a, b in
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zip(self.__clause_element__().clauses,
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other.__composite_values__())])
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# application of custom PropComparator subclasses
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from sqlalchemy.orm import column_property, relationship, composite
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from sqlalchemy import Column, String
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class SomeMappedClass(Base):
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some_column = column_property(Column("some_column", String),
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comparator_factory=MyColumnComparator)
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some_relationship = relationship(SomeOtherClass,
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comparator_factory=MyRelationshipComparator)
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some_composite = composite(
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Column("a", String), Column("b", String),
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comparator_factory=MyCompositeComparator
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)
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Note that for column-level operator redefinition, it's usually
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simpler to define the operators at the Core level, using the
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:attr:`.TypeEngine.comparator_factory` attribute. See
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:ref:`types_operators` for more detail.
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.. seealso::
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:class:`.ColumnProperty.Comparator`
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:class:`.RelationshipProperty.Comparator`
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:class:`.CompositeProperty.Comparator`
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:class:`.ColumnOperators`
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:ref:`types_operators`
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:attr:`.TypeEngine.comparator_factory`
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"""
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__slots__ = "prop", "property", "_parententity", "_adapt_to_entity"
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__visit_name__ = "orm_prop_comparator"
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def __init__(
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self,
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prop,
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parentmapper,
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adapt_to_entity=None,
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):
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self.prop = self.property = prop
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self._parententity = adapt_to_entity or parentmapper
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self._adapt_to_entity = adapt_to_entity
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def __clause_element__(self):
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raise NotImplementedError("%r" % self)
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def _bulk_update_tuples(self, value):
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"""Receive a SQL expression that represents a value in the SET
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clause of an UPDATE statement.
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Return a tuple that can be passed to a :class:`_expression.Update`
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construct.
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"""
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return [(self.__clause_element__(), value)]
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def adapt_to_entity(self, adapt_to_entity):
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"""Return a copy of this PropComparator which will use the given
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:class:`.AliasedInsp` to produce corresponding expressions.
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"""
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return self.__class__(self.prop, self._parententity, adapt_to_entity)
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@property
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def _parentmapper(self):
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"""legacy; this is renamed to _parententity to be
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compatible with QueryableAttribute."""
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return inspect(self._parententity).mapper
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@property
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def _propagate_attrs(self):
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# this suits the case in coercions where we don't actually
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# call ``__clause_element__()`` but still need to get
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# resolved._propagate_attrs. See #6558.
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return util.immutabledict(
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{
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"compile_state_plugin": "orm",
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"plugin_subject": self._parentmapper,
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}
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)
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@property
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def adapter(self):
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"""Produce a callable that adapts column expressions
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to suit an aliased version of this comparator.
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"""
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if self._adapt_to_entity is None:
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return None
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else:
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return self._adapt_to_entity._adapt_element
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@property
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def info(self):
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return self.property.info
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@staticmethod
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def any_op(a, b, **kwargs):
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return a.any(b, **kwargs)
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@staticmethod
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def has_op(a, b, **kwargs):
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return a.has(b, **kwargs)
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@staticmethod
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def of_type_op(a, class_):
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return a.of_type(class_)
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def of_type(self, class_):
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r"""Redefine this object in terms of a polymorphic subclass,
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:func:`_orm.with_polymorphic` construct, or :func:`_orm.aliased`
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construct.
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Returns a new PropComparator from which further criterion can be
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evaluated.
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e.g.::
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query.join(Company.employees.of_type(Engineer)).\
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filter(Engineer.name=='foo')
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:param \class_: a class or mapper indicating that criterion will be
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against this specific subclass.
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.. seealso::
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:ref:`queryguide_join_onclause` - in the :ref:`queryguide_toplevel`
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:ref:`inheritance_of_type`
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"""
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return self.operate(PropComparator.of_type_op, class_)
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def and_(self, *criteria):
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"""Add additional criteria to the ON clause that's represented by this
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relationship attribute.
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E.g.::
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stmt = select(User).join(
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User.addresses.and_(Address.email_address != 'foo')
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)
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stmt = select(User).options(
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joinedload(User.addresses.and_(Address.email_address != 'foo'))
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)
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.. versionadded:: 1.4
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.. seealso::
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:ref:`orm_queryguide_join_on_augmented`
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:ref:`loader_option_criteria`
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:func:`.with_loader_criteria`
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"""
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return self.operate(operators.and_, *criteria)
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def any(self, criterion=None, **kwargs):
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r"""Return true if this collection contains any member that meets the
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given criterion.
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The usual implementation of ``any()`` is
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:meth:`.RelationshipProperty.Comparator.any`.
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:param criterion: an optional ClauseElement formulated against the
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member class' table or attributes.
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:param \**kwargs: key/value pairs corresponding to member class
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attribute names which will be compared via equality to the
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corresponding values.
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"""
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return self.operate(PropComparator.any_op, criterion, **kwargs)
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def has(self, criterion=None, **kwargs):
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r"""Return true if this element references a member which meets the
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given criterion.
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The usual implementation of ``has()`` is
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:meth:`.RelationshipProperty.Comparator.has`.
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:param criterion: an optional ClauseElement formulated against the
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member class' table or attributes.
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:param \**kwargs: key/value pairs corresponding to member class
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attribute names which will be compared via equality to the
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corresponding values.
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"""
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return self.operate(PropComparator.has_op, criterion, **kwargs)
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|
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|
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class StrategizedProperty(MapperProperty):
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"""A MapperProperty which uses selectable strategies to affect
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loading behavior.
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There is a single strategy selected by default. Alternate
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strategies can be selected at Query time through the usage of
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``StrategizedOption`` objects via the Query.options() method.
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The mechanics of StrategizedProperty are used for every Query
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invocation for every mapped attribute participating in that Query,
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to determine first how the attribute will be rendered in SQL
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and secondly how the attribute will retrieve a value from a result
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row and apply it to a mapped object. The routines here are very
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performance-critical.
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"""
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|
__slots__ = (
|
|
"_strategies",
|
|
"strategy",
|
|
"_wildcard_token",
|
|
"_default_path_loader_key",
|
|
)
|
|
inherit_cache = True
|
|
strategy_wildcard_key = None
|
|
|
|
def _memoized_attr__wildcard_token(self):
|
|
return (
|
|
"%s:%s"
|
|
% (self.strategy_wildcard_key, path_registry._WILDCARD_TOKEN),
|
|
)
|
|
|
|
def _memoized_attr__default_path_loader_key(self):
|
|
return (
|
|
"loader",
|
|
(
|
|
"%s:%s"
|
|
% (self.strategy_wildcard_key, path_registry._DEFAULT_TOKEN),
|
|
),
|
|
)
|
|
|
|
def _get_context_loader(self, context, path):
|
|
load = None
|
|
|
|
search_path = path[self]
|
|
|
|
# search among: exact match, "attr.*", "default" strategy
|
|
# if any.
|
|
for path_key in (
|
|
search_path._loader_key,
|
|
search_path._wildcard_path_loader_key,
|
|
search_path._default_path_loader_key,
|
|
):
|
|
if path_key in context.attributes:
|
|
load = context.attributes[path_key]
|
|
break
|
|
|
|
return load
|
|
|
|
def _get_strategy(self, key):
|
|
try:
|
|
return self._strategies[key]
|
|
except KeyError:
|
|
pass
|
|
|
|
# run outside to prevent transfer of exception context
|
|
cls = self._strategy_lookup(self, *key)
|
|
# this previously was setting self._strategies[cls], that's
|
|
# a bad idea; should use strategy key at all times because every
|
|
# strategy has multiple keys at this point
|
|
self._strategies[key] = strategy = cls(self, key)
|
|
return strategy
|
|
|
|
def setup(self, context, query_entity, path, adapter, **kwargs):
|
|
loader = self._get_context_loader(context, path)
|
|
if loader and loader.strategy:
|
|
strat = self._get_strategy(loader.strategy)
|
|
else:
|
|
strat = self.strategy
|
|
strat.setup_query(
|
|
context, query_entity, path, loader, adapter, **kwargs
|
|
)
|
|
|
|
def create_row_processor(
|
|
self, context, query_entity, path, mapper, result, adapter, populators
|
|
):
|
|
loader = self._get_context_loader(context, path)
|
|
if loader and loader.strategy:
|
|
strat = self._get_strategy(loader.strategy)
|
|
else:
|
|
strat = self.strategy
|
|
strat.create_row_processor(
|
|
context,
|
|
query_entity,
|
|
path,
|
|
loader,
|
|
mapper,
|
|
result,
|
|
adapter,
|
|
populators,
|
|
)
|
|
|
|
def do_init(self):
|
|
self._strategies = {}
|
|
self.strategy = self._get_strategy(self.strategy_key)
|
|
|
|
def post_instrument_class(self, mapper):
|
|
if (
|
|
not self.parent.non_primary
|
|
and not mapper.class_manager._attr_has_impl(self.key)
|
|
):
|
|
self.strategy.init_class_attribute(mapper)
|
|
|
|
_all_strategies = collections.defaultdict(dict)
|
|
|
|
@classmethod
|
|
def strategy_for(cls, **kw):
|
|
def decorate(dec_cls):
|
|
# ensure each subclass of the strategy has its
|
|
# own _strategy_keys collection
|
|
if "_strategy_keys" not in dec_cls.__dict__:
|
|
dec_cls._strategy_keys = []
|
|
key = tuple(sorted(kw.items()))
|
|
cls._all_strategies[cls][key] = dec_cls
|
|
dec_cls._strategy_keys.append(key)
|
|
return dec_cls
|
|
|
|
return decorate
|
|
|
|
@classmethod
|
|
def _strategy_lookup(cls, requesting_property, *key):
|
|
requesting_property.parent._with_polymorphic_mappers
|
|
|
|
for prop_cls in cls.__mro__:
|
|
if prop_cls in cls._all_strategies:
|
|
strategies = cls._all_strategies[prop_cls]
|
|
try:
|
|
return strategies[key]
|
|
except KeyError:
|
|
pass
|
|
|
|
for property_type, strats in cls._all_strategies.items():
|
|
if key in strats:
|
|
intended_property_type = property_type
|
|
actual_strategy = strats[key]
|
|
break
|
|
else:
|
|
intended_property_type = None
|
|
actual_strategy = None
|
|
|
|
raise orm_exc.LoaderStrategyException(
|
|
cls,
|
|
requesting_property,
|
|
intended_property_type,
|
|
actual_strategy,
|
|
key,
|
|
)
|
|
|
|
|
|
class ORMOption(ExecutableOption):
|
|
"""Base class for option objects that are passed to ORM queries.
|
|
|
|
These options may be consumed by :meth:`.Query.options`,
|
|
:meth:`.Select.options`, or in a more general sense by any
|
|
:meth:`.Executable.options` method. They are interpreted at
|
|
statement compile time or execution time in modern use. The
|
|
deprecated :class:`.MapperOption` is consumed at ORM query construction
|
|
time.
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
"""
|
|
|
|
__slots__ = ()
|
|
|
|
_is_legacy_option = False
|
|
|
|
propagate_to_loaders = False
|
|
"""if True, indicate this option should be carried along
|
|
to "secondary" SELECT statements that occur for relationship
|
|
lazy loaders as well as attribute load / refresh operations.
|
|
|
|
"""
|
|
|
|
_is_compile_state = False
|
|
|
|
_is_criteria_option = False
|
|
|
|
_is_strategy_option = False
|
|
|
|
|
|
class CompileStateOption(HasCacheKey, ORMOption):
|
|
"""base for :class:`.ORMOption` classes that affect the compilation of
|
|
a SQL query and therefore need to be part of the cache key.
|
|
|
|
.. note:: :class:`.CompileStateOption` is generally non-public and
|
|
should not be used as a base class for user-defined options; instead,
|
|
use :class:`.UserDefinedOption`, which is easier to use as it does not
|
|
interact with ORM compilation internals or caching.
|
|
|
|
:class:`.CompileStateOption` defines an internal attribute
|
|
``_is_compile_state=True`` which has the effect of the ORM compilation
|
|
routines for SELECT and other statements will call upon these options when
|
|
a SQL string is being compiled. As such, these classes implement
|
|
:class:`.HasCacheKey` and need to provide robust ``_cache_key_traversal``
|
|
structures.
|
|
|
|
The :class:`.CompileStateOption` class is used to implement the ORM
|
|
:class:`.LoaderOption` and :class:`.CriteriaOption` classes.
|
|
|
|
.. versionadded:: 1.4.28
|
|
|
|
|
|
"""
|
|
|
|
_is_compile_state = True
|
|
|
|
def process_compile_state(self, compile_state):
|
|
"""Apply a modification to a given :class:`.CompileState`."""
|
|
|
|
def process_compile_state_replaced_entities(
|
|
self, compile_state, mapper_entities
|
|
):
|
|
"""Apply a modification to a given :class:`.CompileState`,
|
|
given entities that were replaced by with_only_columns() or
|
|
with_entities().
|
|
|
|
.. versionadded:: 1.4.19
|
|
|
|
"""
|
|
|
|
|
|
class LoaderOption(CompileStateOption):
|
|
"""Describe a loader modification to an ORM statement at compilation time.
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
"""
|
|
|
|
def process_compile_state_replaced_entities(
|
|
self, compile_state, mapper_entities
|
|
):
|
|
"""Apply a modification to a given :class:`.CompileState`,
|
|
given entities that were replaced by with_only_columns() or
|
|
with_entities().
|
|
|
|
.. versionadded:: 1.4.19
|
|
|
|
"""
|
|
self.process_compile_state(compile_state)
|
|
|
|
def process_compile_state(self, compile_state):
|
|
"""Apply a modification to a given :class:`.CompileState`."""
|
|
|
|
|
|
class CriteriaOption(CompileStateOption):
|
|
"""Describe a WHERE criteria modification to an ORM statement at
|
|
compilation time.
|
|
|
|
.. versionadded:: 1.4
|
|
|
|
"""
|
|
|
|
_is_criteria_option = True
|
|
|
|
def process_compile_state(self, compile_state):
|
|
"""Apply a modification to a given :class:`.CompileState`."""
|
|
|
|
def get_global_criteria(self, attributes):
|
|
"""update additional entity criteria options in the given
|
|
attributes dictionary.
|
|
|
|
"""
|
|
|
|
|
|
class UserDefinedOption(ORMOption):
|
|
"""Base class for a user-defined option that can be consumed from the
|
|
:meth:`.SessionEvents.do_orm_execute` event hook.
|
|
|
|
"""
|
|
|
|
_is_legacy_option = False
|
|
|
|
propagate_to_loaders = False
|
|
"""if True, indicate this option should be carried along
|
|
to "secondary" Query objects produced during lazy loads
|
|
or refresh operations.
|
|
|
|
"""
|
|
|
|
def __init__(self, payload=None):
|
|
self.payload = payload
|
|
|
|
|
|
@util.deprecated_cls(
|
|
"1.4",
|
|
"The :class:`.MapperOption class is deprecated and will be removed "
|
|
"in a future release. For "
|
|
"modifications to queries on a per-execution basis, use the "
|
|
":class:`.UserDefinedOption` class to establish state within a "
|
|
":class:`.Query` or other Core statement, then use the "
|
|
":meth:`.SessionEvents.before_orm_execute` hook to consume them.",
|
|
constructor=None,
|
|
)
|
|
class MapperOption(ORMOption):
|
|
"""Describe a modification to a Query"""
|
|
|
|
_is_legacy_option = True
|
|
|
|
propagate_to_loaders = False
|
|
"""if True, indicate this option should be carried along
|
|
to "secondary" Query objects produced during lazy loads
|
|
or refresh operations.
|
|
|
|
"""
|
|
|
|
def process_query(self, query):
|
|
"""Apply a modification to the given :class:`_query.Query`."""
|
|
|
|
def process_query_conditionally(self, query):
|
|
"""same as process_query(), except that this option may not
|
|
apply to the given query.
|
|
|
|
This is typically applied during a lazy load or scalar refresh
|
|
operation to propagate options stated in the original Query to the
|
|
new Query being used for the load. It occurs for those options that
|
|
specify propagate_to_loaders=True.
|
|
|
|
"""
|
|
|
|
self.process_query(query)
|
|
|
|
|
|
class LoaderStrategy(object):
|
|
"""Describe the loading behavior of a StrategizedProperty object.
|
|
|
|
The ``LoaderStrategy`` interacts with the querying process in three
|
|
ways:
|
|
|
|
* it controls the configuration of the ``InstrumentedAttribute``
|
|
placed on a class to handle the behavior of the attribute. this
|
|
may involve setting up class-level callable functions to fire
|
|
off a select operation when the attribute is first accessed
|
|
(i.e. a lazy load)
|
|
|
|
* it processes the ``QueryContext`` at statement construction time,
|
|
where it can modify the SQL statement that is being produced.
|
|
For example, simple column attributes will add their represented
|
|
column to the list of selected columns, a joined eager loader
|
|
may establish join clauses to add to the statement.
|
|
|
|
* It produces "row processor" functions at result fetching time.
|
|
These "row processor" functions populate a particular attribute
|
|
on a particular mapped instance.
|
|
|
|
"""
|
|
|
|
__slots__ = (
|
|
"parent_property",
|
|
"is_class_level",
|
|
"parent",
|
|
"key",
|
|
"strategy_key",
|
|
"strategy_opts",
|
|
)
|
|
|
|
def __init__(self, parent, strategy_key):
|
|
self.parent_property = parent
|
|
self.is_class_level = False
|
|
self.parent = self.parent_property.parent
|
|
self.key = self.parent_property.key
|
|
self.strategy_key = strategy_key
|
|
self.strategy_opts = dict(strategy_key)
|
|
|
|
def init_class_attribute(self, mapper):
|
|
pass
|
|
|
|
def setup_query(
|
|
self, compile_state, query_entity, path, loadopt, adapter, **kwargs
|
|
):
|
|
"""Establish column and other state for a given QueryContext.
|
|
|
|
This method fulfills the contract specified by MapperProperty.setup().
|
|
|
|
StrategizedProperty delegates its setup() method
|
|
directly to this method.
|
|
|
|
"""
|
|
|
|
def create_row_processor(
|
|
self,
|
|
context,
|
|
query_entity,
|
|
path,
|
|
loadopt,
|
|
mapper,
|
|
result,
|
|
adapter,
|
|
populators,
|
|
):
|
|
"""Establish row processing functions for a given QueryContext.
|
|
|
|
This method fulfills the contract specified by
|
|
MapperProperty.create_row_processor().
|
|
|
|
StrategizedProperty delegates its create_row_processor() method
|
|
directly to this method.
|
|
|
|
"""
|
|
|
|
def __str__(self):
|
|
return str(self.parent_property)
|