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577 lines
19 KiB
Python
577 lines
19 KiB
Python
# orm/interfaces.py
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# Copyright (C) 2005-2014 the SQLAlchemy authors and contributors <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: http://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 the now deprecated ORM extension classes as well
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as ORM internals.
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Other than the deprecated extensions, this module and the
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classes within should be considered mostly private.
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"""
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from __future__ import absolute_import
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from .. import exc as sa_exc, util, inspect
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from ..sql import operators
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from collections import deque
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from .base import ONETOMANY, MANYTOONE, MANYTOMANY, EXT_CONTINUE, EXT_STOP, NOT_EXTENSION
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from .base import _InspectionAttr, _MappedAttribute
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from .path_registry import PathRegistry
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import collections
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__all__ = (
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'AttributeExtension',
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'EXT_CONTINUE',
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'EXT_STOP',
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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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'MapperExtension',
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'MapperOption',
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'MapperProperty',
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'PropComparator',
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'SessionExtension',
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'StrategizedProperty',
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)
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class MapperProperty(_MappedAttribute, _InspectionAttr):
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"""Manage the relationship of a ``Mapper`` to a single class
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attribute, as well as that attribute as it appears on individual
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instances of the class, including attribute instrumentation,
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attribute access, loading behavior, and dependency calculations.
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The most common occurrences of :class:`.MapperProperty` are the
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mapped :class:`.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:`.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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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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"""
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is_property = True
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def setup(self, context, 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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pass
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def create_row_processor(self, context, path,
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mapper, row, adapter):
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"""Return a 3-tuple consisting of three row processing functions.
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"""
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return None, None, None
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def cascade_iterator(self, type_, state, visited_instances=None,
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halt_on=None):
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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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See PropertyLoader for the related instance implementation.
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"""
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return iter(())
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def set_parent(self, parent, init):
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self.parent = parent
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def instrument_class(self, mapper): # pragma: no-coverage
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raise NotImplementedError()
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@util.memoized_property
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def 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:`.MapperProperty`.
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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:`.relationship`, or :func:`.composite`
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functions.
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.. versionadded:: 0.8 Added support for .info to all
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:class:`.MapperProperty` subclasses.
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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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_configure_started = False
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_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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pass
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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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"""
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pass
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def is_primary(self):
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"""Return True if this ``MapperProperty``'s mapper is the
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primary mapper for its class.
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This flag is used to indicate that the ``MapperProperty`` can
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define attribute instrumentation for the class at the class
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level (as opposed to the individual instance level).
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"""
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return not self.parent.non_primary
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def merge(self, session, source_state, source_dict, dest_state,
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dest_dict, load, _recursive):
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"""Merge the attribute represented by this ``MapperProperty``
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from source to destination object"""
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pass
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def compare(self, operator, value, **kw):
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"""Return a compare operation for the columns represented by
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this ``MapperProperty`` to the given value, which may be a
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column value or an instance. 'operator' is an operator from
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the operators module, or from sql.Comparator.
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By default uses the PropComparator attached to this MapperProperty
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under the attribute name "comparator".
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"""
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return operator(self.comparator, value)
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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), getattr(self, 'key', 'no key'))
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class PropComparator(operators.ColumnOperators):
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"""Defines boolean, comparison, and other operators for
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: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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See also:
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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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def __init__(self, prop, parentmapper, adapt_to_entity=None):
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self.prop = self.property = prop
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self._parentmapper = 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 _query_clause_element(self):
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return self.__clause_element__()
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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._parentmapper, adapt_to_entity)
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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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@util.memoized_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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"""Redefine this object in terms of a polymorphic subclass.
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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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"""
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return self.operate(PropComparator.of_type_op, class_)
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def any(self, criterion=None, **kwargs):
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"""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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"""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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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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"""
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strategy_wildcard_key = None
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def _get_context_loader(self, context, path):
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load = None
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# use EntityRegistry.__getitem__()->PropRegistry here so
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# that the path is stated in terms of our base
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search_path = dict.__getitem__(path, self)
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# search among: exact match, "attr.*", "default" strategy
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# if any.
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for path_key in (
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search_path._loader_key,
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search_path._wildcard_path_loader_key,
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search_path._default_path_loader_key
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):
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if path_key in context.attributes:
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load = context.attributes[path_key]
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break
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return load
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def _get_strategy(self, key):
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try:
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return self._strategies[key]
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except KeyError:
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cls = self._strategy_lookup(*key)
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self._strategies[key] = self._strategies[cls] = strategy = cls(self)
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return strategy
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def _get_strategy_by_cls(self, cls):
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return self._get_strategy(cls._strategy_keys[0])
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def setup(self, context, entity, path, adapter, **kwargs):
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loader = self._get_context_loader(context, path)
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if loader and loader.strategy:
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strat = self._get_strategy(loader.strategy)
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else:
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strat = self.strategy
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strat.setup_query(context, entity, path, loader, adapter, **kwargs)
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def create_row_processor(self, context, path, mapper, row, adapter):
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loader = self._get_context_loader(context, path)
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if loader and loader.strategy:
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strat = self._get_strategy(loader.strategy)
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else:
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strat = self.strategy
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return strat.create_row_processor(context, path, loader,
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mapper, row, adapter)
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def do_init(self):
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self._strategies = {}
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self.strategy = self._get_strategy_by_cls(self.strategy_class)
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def post_instrument_class(self, mapper):
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if self.is_primary() and \
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not mapper.class_manager._attr_has_impl(self.key):
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self.strategy.init_class_attribute(mapper)
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_strategies = collections.defaultdict(dict)
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@classmethod
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def strategy_for(cls, **kw):
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def decorate(dec_cls):
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dec_cls._strategy_keys = []
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key = tuple(sorted(kw.items()))
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cls._strategies[cls][key] = dec_cls
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dec_cls._strategy_keys.append(key)
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return dec_cls
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return decorate
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@classmethod
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def _strategy_lookup(cls, *key):
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for prop_cls in cls.__mro__:
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if prop_cls in cls._strategies:
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strategies = cls._strategies[prop_cls]
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try:
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return strategies[key]
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except KeyError:
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pass
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raise Exception("can't locate strategy for %s %s" % (cls, key))
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class MapperOption(object):
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"""Describe a modification to a Query."""
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propagate_to_loaders = False
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"""if True, indicate this option should be carried along
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Query object generated by scalar or object lazy loaders.
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"""
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def process_query(self, query):
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pass
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def process_query_conditionally(self, query):
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"""same as process_query(), except that this option may not
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apply to the given query.
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Used when secondary loaders resend existing options to a new
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Query."""
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self.process_query(query)
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class LoaderStrategy(object):
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"""Describe the loading behavior of a StrategizedProperty object.
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The ``LoaderStrategy`` interacts with the querying process in three
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ways:
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* it controls the configuration of the ``InstrumentedAttribute``
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placed on a class to handle the behavior of the attribute. this
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may involve setting up class-level callable functions to fire
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off a select operation when the attribute is first accessed
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(i.e. a lazy load)
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* it processes the ``QueryContext`` at statement construction time,
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where it can modify the SQL statement that is being produced.
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Simple column attributes may add their represented column to the
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list of selected columns, *eager loading* properties may add
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``LEFT OUTER JOIN`` clauses to the statement.
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* It produces "row processor" functions at result fetching time.
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These "row processor" functions populate a particular attribute
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on a particular mapped instance.
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"""
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def __init__(self, parent):
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self.parent_property = parent
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self.is_class_level = False
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self.parent = self.parent_property.parent
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self.key = self.parent_property.key
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def init_class_attribute(self, mapper):
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pass
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def setup_query(self, context, entity, path, loadopt, adapter, **kwargs):
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pass
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def create_row_processor(self, context, path, loadopt, mapper,
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row, adapter):
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"""Return row processing functions which fulfill the contract
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specified by MapperProperty.create_row_processor.
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StrategizedProperty delegates its create_row_processor method
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directly to this method. """
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return None, None, None
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def __str__(self):
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return str(self.parent_property)
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