1117 lines
48 KiB
Python
1117 lines
48 KiB
Python
"""
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Accessors for related objects.
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When a field defines a relation between two models, each model class provides
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an attribute to access related instances of the other model class (unless the
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reverse accessor has been disabled with related_name='+').
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Accessors are implemented as descriptors in order to customize access and
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assignment. This module defines the descriptor classes.
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Forward accessors follow foreign keys. Reverse accessors trace them back. For
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example, with the following models::
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class Parent(Model):
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pass
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class Child(Model):
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parent = ForeignKey(Parent, related_name='children')
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``child.parent`` is a forward many-to-one relation. ``parent.children`` is a
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reverse many-to-one relation.
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There are three types of relations (many-to-one, one-to-one, and many-to-many)
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and two directions (forward and reverse) for a total of six combinations.
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1. Related instance on the forward side of a many-to-one relation:
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``ForwardManyToOneDescriptor``.
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Uniqueness of foreign key values is irrelevant to accessing the related
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instance, making the many-to-one and one-to-one cases identical as far as
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the descriptor is concerned. The constraint is checked upstream (unicity
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validation in forms) or downstream (unique indexes in the database).
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2. Related instance on the forward side of a one-to-one
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relation: ``ForwardOneToOneDescriptor``.
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It avoids querying the database when accessing the parent link field in
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a multi-table inheritance scenario.
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3. Related instance on the reverse side of a one-to-one relation:
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``ReverseOneToOneDescriptor``.
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One-to-one relations are asymmetrical, despite the apparent symmetry of the
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name, because they're implemented in the database with a foreign key from
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one table to another. As a consequence ``ReverseOneToOneDescriptor`` is
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slightly different from ``ForwardManyToOneDescriptor``.
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4. Related objects manager for related instances on the reverse side of a
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many-to-one relation: ``ReverseManyToOneDescriptor``.
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Unlike the previous two classes, this one provides access to a collection
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of objects. It returns a manager rather than an instance.
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5. Related objects manager for related instances on the forward or reverse
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sides of a many-to-many relation: ``ManyToManyDescriptor``.
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Many-to-many relations are symmetrical. The syntax of Django models
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requires declaring them on one side but that's an implementation detail.
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They could be declared on the other side without any change in behavior.
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Therefore the forward and reverse descriptors can be the same.
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If you're looking for ``ForwardManyToManyDescriptor`` or
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``ReverseManyToManyDescriptor``, use ``ManyToManyDescriptor`` instead.
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"""
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from operator import attrgetter
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from django.db import connections, router, transaction
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from django.db.models import Q, signals
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from django.db.models.query import QuerySet
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from django.utils.functional import cached_property
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class ForwardManyToOneDescriptor:
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"""
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Accessor to the related object on the forward side of a many-to-one or
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one-to-one (via ForwardOneToOneDescriptor subclass) relation.
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In the example::
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class Child(Model):
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parent = ForeignKey(Parent, related_name='children')
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``child.parent`` is a ``ForwardManyToOneDescriptor`` instance.
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"""
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def __init__(self, field_with_rel):
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self.field = field_with_rel
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self.cache_name = self.field.get_cache_name()
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@cached_property
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def RelatedObjectDoesNotExist(self):
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# The exception can't be created at initialization time since the
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# related model might not be resolved yet; `rel.model` might still be
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# a string model reference.
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return type(
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'RelatedObjectDoesNotExist',
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(self.field.remote_field.model.DoesNotExist, AttributeError),
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{}
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)
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def is_cached(self, instance):
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return hasattr(instance, self.cache_name)
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def get_queryset(self, **hints):
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return self.field.remote_field.model._base_manager.db_manager(hints=hints).all()
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def get_prefetch_queryset(self, instances, queryset=None):
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if queryset is None:
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queryset = self.get_queryset()
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queryset._add_hints(instance=instances[0])
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rel_obj_attr = self.field.get_foreign_related_value
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instance_attr = self.field.get_local_related_value
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instances_dict = {instance_attr(inst): inst for inst in instances}
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related_field = self.field.foreign_related_fields[0]
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# FIXME: This will need to be revisited when we introduce support for
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# composite fields. In the meantime we take this practical approach to
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# solve a regression on 1.6 when the reverse manager in hidden
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# (related_name ends with a '+'). Refs #21410.
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# The check for len(...) == 1 is a special case that allows the query
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# to be join-less and smaller. Refs #21760.
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if self.field.remote_field.is_hidden() or len(self.field.foreign_related_fields) == 1:
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query = {'%s__in' % related_field.name: {instance_attr(inst)[0] for inst in instances}}
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else:
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query = {'%s__in' % self.field.related_query_name(): instances}
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queryset = queryset.filter(**query)
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# Since we're going to assign directly in the cache,
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# we must manage the reverse relation cache manually.
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if not self.field.remote_field.multiple:
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rel_obj_cache_name = self.field.remote_field.get_cache_name()
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for rel_obj in queryset:
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instance = instances_dict[rel_obj_attr(rel_obj)]
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setattr(rel_obj, rel_obj_cache_name, instance)
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return queryset, rel_obj_attr, instance_attr, True, self.cache_name
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def get_object(self, instance):
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qs = self.get_queryset(instance=instance)
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# Assuming the database enforces foreign keys, this won't fail.
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return qs.get(self.field.get_reverse_related_filter(instance))
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def __get__(self, instance, cls=None):
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"""
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Get the related instance through the forward relation.
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With the example above, when getting ``child.parent``:
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- ``self`` is the descriptor managing the ``parent`` attribute
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- ``instance`` is the ``child`` instance
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- ``cls`` is the ``Child`` class (we don't need it)
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"""
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if instance is None:
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return self
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# The related instance is loaded from the database and then cached in
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# the attribute defined in self.cache_name. It can also be pre-cached
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# by the reverse accessor (ReverseOneToOneDescriptor).
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try:
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rel_obj = getattr(instance, self.cache_name)
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except AttributeError:
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val = self.field.get_local_related_value(instance)
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if None in val:
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rel_obj = None
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else:
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rel_obj = self.get_object(instance)
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# If this is a one-to-one relation, set the reverse accessor
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# cache on the related object to the current instance to avoid
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# an extra SQL query if it's accessed later on.
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if not self.field.remote_field.multiple:
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setattr(rel_obj, self.field.remote_field.get_cache_name(), instance)
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setattr(instance, self.cache_name, rel_obj)
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if rel_obj is None and not self.field.null:
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raise self.RelatedObjectDoesNotExist(
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"%s has no %s." % (self.field.model.__name__, self.field.name)
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)
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else:
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return rel_obj
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def __set__(self, instance, value):
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"""
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Set the related instance through the forward relation.
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With the example above, when setting ``child.parent = parent``:
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- ``self`` is the descriptor managing the ``parent`` attribute
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- ``instance`` is the ``child`` instance
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- ``value`` is the ``parent`` instance on the right of the equal sign
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"""
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# An object must be an instance of the related class.
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if value is not None and not isinstance(value, self.field.remote_field.model._meta.concrete_model):
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raise ValueError(
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'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
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value,
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instance._meta.object_name,
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self.field.name,
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self.field.remote_field.model._meta.object_name,
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)
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)
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elif value is not None:
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if instance._state.db is None:
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instance._state.db = router.db_for_write(instance.__class__, instance=value)
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elif value._state.db is None:
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value._state.db = router.db_for_write(value.__class__, instance=instance)
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elif value._state.db is not None and instance._state.db is not None:
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if not router.allow_relation(value, instance):
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raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)
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# If we're setting the value of a OneToOneField to None, we need to clear
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# out the cache on any old related object. Otherwise, deleting the
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# previously-related object will also cause this object to be deleted,
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# which is wrong.
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if value is None:
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# Look up the previously-related object, which may still be available
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# since we've not yet cleared out the related field.
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# Use the cache directly, instead of the accessor; if we haven't
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# populated the cache, then we don't care - we're only accessing
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# the object to invalidate the accessor cache, so there's no
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# need to populate the cache just to expire it again.
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related = getattr(instance, self.cache_name, None)
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# If we've got an old related object, we need to clear out its
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# cache. This cache also might not exist if the related object
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# hasn't been accessed yet.
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if related is not None:
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setattr(related, self.field.remote_field.get_cache_name(), None)
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for lh_field, rh_field in self.field.related_fields:
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setattr(instance, lh_field.attname, None)
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# Set the values of the related field.
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else:
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for lh_field, rh_field in self.field.related_fields:
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setattr(instance, lh_field.attname, getattr(value, rh_field.attname))
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# Set the related instance cache used by __get__ to avoid an SQL query
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# when accessing the attribute we just set.
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setattr(instance, self.cache_name, value)
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# If this is a one-to-one relation, set the reverse accessor cache on
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# the related object to the current instance to avoid an extra SQL
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# query if it's accessed later on.
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if value is not None and not self.field.remote_field.multiple:
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setattr(value, self.field.remote_field.get_cache_name(), instance)
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class ForwardOneToOneDescriptor(ForwardManyToOneDescriptor):
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"""
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Accessor to the related object on the forward side of a one-to-one relation.
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In the example::
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class Restaurant(Model):
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place = OneToOneField(Place, related_name='restaurant')
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``restaurant.place`` is a ``ForwardOneToOneDescriptor`` instance.
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"""
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def get_object(self, instance):
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if self.field.remote_field.parent_link:
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deferred = instance.get_deferred_fields()
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# Because it's a parent link, all the data is available in the
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# instance, so populate the parent model with this data.
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rel_model = self.field.remote_field.model
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fields = [field.attname for field in rel_model._meta.concrete_fields]
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# If any of the related model's fields are deferred, fallback to
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# fetching all fields from the related model. This avoids a query
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# on the related model for every deferred field.
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if not any(field in fields for field in deferred):
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kwargs = {field: getattr(instance, field) for field in fields}
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obj = rel_model(**kwargs)
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obj._state.adding = instance._state.adding
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obj._state.db = instance._state.db
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return obj
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return super().get_object(instance)
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def __set__(self, instance, value):
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super().__set__(instance, value)
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# If the primary key is a link to a parent model and a parent instance
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# is being set, update the value of the inherited pk(s).
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if self.field.primary_key and self.field.remote_field.parent_link:
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opts = instance._meta
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# Inherited primary key fields from this object's base classes.
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inherited_pk_fields = [
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field for field in opts.concrete_fields
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if field.primary_key and field.remote_field
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]
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for field in inherited_pk_fields:
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rel_model_pk_name = field.remote_field.model._meta.pk.attname
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raw_value = getattr(value, rel_model_pk_name) if value is not None else None
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setattr(instance, rel_model_pk_name, raw_value)
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class ReverseOneToOneDescriptor:
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"""
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Accessor to the related object on the reverse side of a one-to-one
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relation.
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In the example::
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class Restaurant(Model):
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place = OneToOneField(Place, related_name='restaurant')
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``place.restaurant`` is a ``ReverseOneToOneDescriptor`` instance.
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"""
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def __init__(self, related):
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self.related = related
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self.cache_name = related.get_cache_name()
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@cached_property
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def RelatedObjectDoesNotExist(self):
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# The exception isn't created at initialization time for the sake of
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# consistency with `ForwardManyToOneDescriptor`.
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return type(
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'RelatedObjectDoesNotExist',
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(self.related.related_model.DoesNotExist, AttributeError),
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{}
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)
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def is_cached(self, instance):
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return hasattr(instance, self.cache_name)
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def get_queryset(self, **hints):
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return self.related.related_model._base_manager.db_manager(hints=hints).all()
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def get_prefetch_queryset(self, instances, queryset=None):
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if queryset is None:
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queryset = self.get_queryset()
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queryset._add_hints(instance=instances[0])
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rel_obj_attr = attrgetter(self.related.field.attname)
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def instance_attr(obj):
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return obj.pk
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instances_dict = {instance_attr(inst): inst for inst in instances}
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query = {'%s__in' % self.related.field.name: instances}
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queryset = queryset.filter(**query)
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# Since we're going to assign directly in the cache,
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# we must manage the reverse relation cache manually.
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rel_obj_cache_name = self.related.field.get_cache_name()
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for rel_obj in queryset:
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instance = instances_dict[rel_obj_attr(rel_obj)]
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setattr(rel_obj, rel_obj_cache_name, instance)
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return queryset, rel_obj_attr, instance_attr, True, self.cache_name
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def __get__(self, instance, cls=None):
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"""
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Get the related instance through the reverse relation.
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With the example above, when getting ``place.restaurant``:
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- ``self`` is the descriptor managing the ``restaurant`` attribute
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- ``instance`` is the ``place`` instance
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- ``cls`` is the ``Place`` class (unused)
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Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
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"""
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if instance is None:
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return self
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# The related instance is loaded from the database and then cached in
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# the attribute defined in self.cache_name. It can also be pre-cached
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# by the forward accessor (ForwardManyToOneDescriptor).
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try:
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rel_obj = getattr(instance, self.cache_name)
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except AttributeError:
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related_pk = instance.pk
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if related_pk is None:
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rel_obj = None
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else:
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filter_args = self.related.field.get_forward_related_filter(instance)
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try:
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rel_obj = self.get_queryset(instance=instance).get(**filter_args)
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except self.related.related_model.DoesNotExist:
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rel_obj = None
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else:
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# Set the forward accessor cache on the related object to
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# the current instance to avoid an extra SQL query if it's
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# accessed later on.
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setattr(rel_obj, self.related.field.get_cache_name(), instance)
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setattr(instance, self.cache_name, rel_obj)
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if rel_obj is None:
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raise self.RelatedObjectDoesNotExist(
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"%s has no %s." % (
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instance.__class__.__name__,
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self.related.get_accessor_name()
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)
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)
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else:
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return rel_obj
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def __set__(self, instance, value):
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"""
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Set the related instance through the reverse relation.
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With the example above, when setting ``place.restaurant = restaurant``:
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- ``self`` is the descriptor managing the ``restaurant`` attribute
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- ``instance`` is the ``place`` instance
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- ``value`` is the ``restaurant`` instance on the right of the equal sign
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Keep in mind that ``Restaurant`` holds the foreign key to ``Place``.
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"""
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# The similarity of the code below to the code in
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# ForwardManyToOneDescriptor is annoying, but there's a bunch
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# of small differences that would make a common base class convoluted.
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if value is None:
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# Update the cached related instance (if any) & clear the cache.
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try:
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rel_obj = getattr(instance, self.cache_name)
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except AttributeError:
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pass
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else:
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delattr(instance, self.cache_name)
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setattr(rel_obj, self.related.field.name, None)
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elif not isinstance(value, self.related.related_model):
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# An object must be an instance of the related class.
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raise ValueError(
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'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
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value,
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instance._meta.object_name,
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self.related.get_accessor_name(),
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self.related.related_model._meta.object_name,
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)
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)
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else:
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if instance._state.db is None:
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instance._state.db = router.db_for_write(instance.__class__, instance=value)
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elif value._state.db is None:
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value._state.db = router.db_for_write(value.__class__, instance=instance)
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elif value._state.db is not None and instance._state.db is not None:
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if not router.allow_relation(value, instance):
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raise ValueError('Cannot assign "%r": the current database router prevents this relation.' % value)
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related_pk = tuple(getattr(instance, field.attname) for field in self.related.field.foreign_related_fields)
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# Set the value of the related field to the value of the related object's related field
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for index, field in enumerate(self.related.field.local_related_fields):
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setattr(value, field.attname, related_pk[index])
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# Set the related instance cache used by __get__ to avoid an SQL query
|
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# when accessing the attribute we just set.
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setattr(instance, self.cache_name, value)
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# Set the forward accessor cache on the related object to the current
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# instance to avoid an extra SQL query if it's accessed later on.
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setattr(value, self.related.field.get_cache_name(), instance)
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|
|
|
|
class ReverseManyToOneDescriptor:
|
|
"""
|
|
Accessor to the related objects manager on the reverse side of a
|
|
many-to-one relation.
|
|
|
|
In the example::
|
|
|
|
class Child(Model):
|
|
parent = ForeignKey(Parent, related_name='children')
|
|
|
|
``parent.children`` is a ``ReverseManyToOneDescriptor`` instance.
|
|
|
|
Most of the implementation is delegated to a dynamically defined manager
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class built by ``create_forward_many_to_many_manager()`` defined below.
|
|
"""
|
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|
|
def __init__(self, rel):
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self.rel = rel
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self.field = rel.field
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|
|
@cached_property
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|
def related_manager_cls(self):
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related_model = self.rel.related_model
|
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return create_reverse_many_to_one_manager(
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related_model._default_manager.__class__,
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self.rel,
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)
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def __get__(self, instance, cls=None):
|
|
"""
|
|
Get the related objects through the reverse relation.
|
|
|
|
With the example above, when getting ``parent.children``:
|
|
|
|
- ``self`` is the descriptor managing the ``children`` attribute
|
|
- ``instance`` is the ``parent`` instance
|
|
- ``cls`` is the ``Parent`` class (unused)
|
|
"""
|
|
if instance is None:
|
|
return self
|
|
|
|
return self.related_manager_cls(instance)
|
|
|
|
def _get_set_deprecation_msg_params(self):
|
|
return (
|
|
'reverse side of a related set',
|
|
self.rel.get_accessor_name(),
|
|
)
|
|
|
|
def __set__(self, instance, value):
|
|
raise TypeError(
|
|
'Direct assignment to the %s is prohibited. Use %s.set() instead.'
|
|
% self._get_set_deprecation_msg_params(),
|
|
)
|
|
|
|
|
|
def create_reverse_many_to_one_manager(superclass, rel):
|
|
"""
|
|
Create a manager for the reverse side of a many-to-one relation.
|
|
|
|
This manager subclasses another manager, generally the default manager of
|
|
the related model, and adds behaviors specific to many-to-one relations.
|
|
"""
|
|
|
|
class RelatedManager(superclass):
|
|
def __init__(self, instance):
|
|
super().__init__()
|
|
|
|
self.instance = instance
|
|
self.model = rel.related_model
|
|
self.field = rel.field
|
|
|
|
self.core_filters = {self.field.name: instance}
|
|
|
|
def __call__(self, *, manager):
|
|
manager = getattr(self.model, manager)
|
|
manager_class = create_reverse_many_to_one_manager(manager.__class__, rel)
|
|
return manager_class(self.instance)
|
|
do_not_call_in_templates = True
|
|
|
|
def _apply_rel_filters(self, queryset):
|
|
"""
|
|
Filter the queryset for the instance this manager is bound to.
|
|
"""
|
|
db = self._db or router.db_for_read(self.model, instance=self.instance)
|
|
empty_strings_as_null = connections[db].features.interprets_empty_strings_as_nulls
|
|
queryset._add_hints(instance=self.instance)
|
|
if self._db:
|
|
queryset = queryset.using(self._db)
|
|
queryset = queryset.filter(**self.core_filters)
|
|
for field in self.field.foreign_related_fields:
|
|
val = getattr(self.instance, field.attname)
|
|
if val is None or (val == '' and empty_strings_as_null):
|
|
return queryset.none()
|
|
queryset._known_related_objects = {self.field: {self.instance.pk: self.instance}}
|
|
return queryset
|
|
|
|
def _remove_prefetched_objects(self):
|
|
try:
|
|
self.instance._prefetched_objects_cache.pop(self.field.related_query_name())
|
|
except (AttributeError, KeyError):
|
|
pass # nothing to clear from cache
|
|
|
|
def get_queryset(self):
|
|
try:
|
|
return self.instance._prefetched_objects_cache[self.field.related_query_name()]
|
|
except (AttributeError, KeyError):
|
|
queryset = super().get_queryset()
|
|
return self._apply_rel_filters(queryset)
|
|
|
|
def get_prefetch_queryset(self, instances, queryset=None):
|
|
if queryset is None:
|
|
queryset = super().get_queryset()
|
|
|
|
queryset._add_hints(instance=instances[0])
|
|
queryset = queryset.using(queryset._db or self._db)
|
|
|
|
rel_obj_attr = self.field.get_local_related_value
|
|
instance_attr = self.field.get_foreign_related_value
|
|
instances_dict = {instance_attr(inst): inst for inst in instances}
|
|
query = {'%s__in' % self.field.name: instances}
|
|
queryset = queryset.filter(**query)
|
|
|
|
# Since we just bypassed this class' get_queryset(), we must manage
|
|
# the reverse relation manually.
|
|
for rel_obj in queryset:
|
|
instance = instances_dict[rel_obj_attr(rel_obj)]
|
|
setattr(rel_obj, self.field.name, instance)
|
|
cache_name = self.field.related_query_name()
|
|
return queryset, rel_obj_attr, instance_attr, False, cache_name
|
|
|
|
def add(self, *objs, bulk=True):
|
|
self._remove_prefetched_objects()
|
|
objs = list(objs)
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
|
|
def check_and_update_obj(obj):
|
|
if not isinstance(obj, self.model):
|
|
raise TypeError("'%s' instance expected, got %r" % (
|
|
self.model._meta.object_name, obj,
|
|
))
|
|
setattr(obj, self.field.name, self.instance)
|
|
|
|
if bulk:
|
|
pks = []
|
|
for obj in objs:
|
|
check_and_update_obj(obj)
|
|
if obj._state.adding or obj._state.db != db:
|
|
raise ValueError(
|
|
"%r instance isn't saved. Use bulk=False or save "
|
|
"the object first." % obj
|
|
)
|
|
pks.append(obj.pk)
|
|
self.model._base_manager.using(db).filter(pk__in=pks).update(**{
|
|
self.field.name: self.instance,
|
|
})
|
|
else:
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
for obj in objs:
|
|
check_and_update_obj(obj)
|
|
obj.save()
|
|
add.alters_data = True
|
|
|
|
def create(self, **kwargs):
|
|
kwargs[self.field.name] = self.instance
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
return super(RelatedManager, self.db_manager(db)).create(**kwargs)
|
|
create.alters_data = True
|
|
|
|
def get_or_create(self, **kwargs):
|
|
kwargs[self.field.name] = self.instance
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
return super(RelatedManager, self.db_manager(db)).get_or_create(**kwargs)
|
|
get_or_create.alters_data = True
|
|
|
|
def update_or_create(self, **kwargs):
|
|
kwargs[self.field.name] = self.instance
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
return super(RelatedManager, self.db_manager(db)).update_or_create(**kwargs)
|
|
update_or_create.alters_data = True
|
|
|
|
# remove() and clear() are only provided if the ForeignKey can have a value of null.
|
|
if rel.field.null:
|
|
def remove(self, *objs, bulk=True):
|
|
if not objs:
|
|
return
|
|
val = self.field.get_foreign_related_value(self.instance)
|
|
old_ids = set()
|
|
for obj in objs:
|
|
# Is obj actually part of this descriptor set?
|
|
if self.field.get_local_related_value(obj) == val:
|
|
old_ids.add(obj.pk)
|
|
else:
|
|
raise self.field.remote_field.model.DoesNotExist(
|
|
"%r is not related to %r." % (obj, self.instance)
|
|
)
|
|
self._clear(self.filter(pk__in=old_ids), bulk)
|
|
remove.alters_data = True
|
|
|
|
def clear(self, *, bulk=True):
|
|
self._clear(self, bulk)
|
|
clear.alters_data = True
|
|
|
|
def _clear(self, queryset, bulk):
|
|
self._remove_prefetched_objects()
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
queryset = queryset.using(db)
|
|
if bulk:
|
|
# `QuerySet.update()` is intrinsically atomic.
|
|
queryset.update(**{self.field.name: None})
|
|
else:
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
for obj in queryset:
|
|
setattr(obj, self.field.name, None)
|
|
obj.save(update_fields=[self.field.name])
|
|
_clear.alters_data = True
|
|
|
|
def set(self, objs, *, bulk=True, clear=False):
|
|
# Force evaluation of `objs` in case it's a queryset whose value
|
|
# could be affected by `manager.clear()`. Refs #19816.
|
|
objs = tuple(objs)
|
|
|
|
if self.field.null:
|
|
db = router.db_for_write(self.model, instance=self.instance)
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
if clear:
|
|
self.clear()
|
|
self.add(*objs, bulk=bulk)
|
|
else:
|
|
old_objs = set(self.using(db).all())
|
|
new_objs = []
|
|
for obj in objs:
|
|
if obj in old_objs:
|
|
old_objs.remove(obj)
|
|
else:
|
|
new_objs.append(obj)
|
|
|
|
self.remove(*old_objs, bulk=bulk)
|
|
self.add(*new_objs, bulk=bulk)
|
|
else:
|
|
self.add(*objs, bulk=bulk)
|
|
set.alters_data = True
|
|
|
|
return RelatedManager
|
|
|
|
|
|
class ManyToManyDescriptor(ReverseManyToOneDescriptor):
|
|
"""
|
|
Accessor to the related objects manager on the forward and reverse sides of
|
|
a many-to-many relation.
|
|
|
|
In the example::
|
|
|
|
class Pizza(Model):
|
|
toppings = ManyToManyField(Topping, related_name='pizzas')
|
|
|
|
``pizza.toppings`` and ``topping.pizzas`` are ``ManyToManyDescriptor``
|
|
instances.
|
|
|
|
Most of the implementation is delegated to a dynamically defined manager
|
|
class built by ``create_forward_many_to_many_manager()`` defined below.
|
|
"""
|
|
|
|
def __init__(self, rel, reverse=False):
|
|
super().__init__(rel)
|
|
|
|
self.reverse = reverse
|
|
|
|
@property
|
|
def through(self):
|
|
# through is provided so that you have easy access to the through
|
|
# model (Book.authors.through) for inlines, etc. This is done as
|
|
# a property to ensure that the fully resolved value is returned.
|
|
return self.rel.through
|
|
|
|
@cached_property
|
|
def related_manager_cls(self):
|
|
related_model = self.rel.related_model if self.reverse else self.rel.model
|
|
|
|
return create_forward_many_to_many_manager(
|
|
related_model._default_manager.__class__,
|
|
self.rel,
|
|
reverse=self.reverse,
|
|
)
|
|
|
|
def _get_set_deprecation_msg_params(self):
|
|
return (
|
|
'%s side of a many-to-many set' % ('reverse' if self.reverse else 'forward'),
|
|
self.rel.get_accessor_name() if self.reverse else self.field.name,
|
|
)
|
|
|
|
|
|
def create_forward_many_to_many_manager(superclass, rel, reverse):
|
|
"""
|
|
Create a manager for the either side of a many-to-many relation.
|
|
|
|
This manager subclasses another manager, generally the default manager of
|
|
the related model, and adds behaviors specific to many-to-many relations.
|
|
"""
|
|
|
|
class ManyRelatedManager(superclass):
|
|
def __init__(self, instance=None):
|
|
super().__init__()
|
|
|
|
self.instance = instance
|
|
|
|
if not reverse:
|
|
self.model = rel.model
|
|
self.query_field_name = rel.field.related_query_name()
|
|
self.prefetch_cache_name = rel.field.name
|
|
self.source_field_name = rel.field.m2m_field_name()
|
|
self.target_field_name = rel.field.m2m_reverse_field_name()
|
|
self.symmetrical = rel.symmetrical
|
|
else:
|
|
self.model = rel.related_model
|
|
self.query_field_name = rel.field.name
|
|
self.prefetch_cache_name = rel.field.related_query_name()
|
|
self.source_field_name = rel.field.m2m_reverse_field_name()
|
|
self.target_field_name = rel.field.m2m_field_name()
|
|
self.symmetrical = False
|
|
|
|
self.through = rel.through
|
|
self.reverse = reverse
|
|
|
|
self.source_field = self.through._meta.get_field(self.source_field_name)
|
|
self.target_field = self.through._meta.get_field(self.target_field_name)
|
|
|
|
self.core_filters = {}
|
|
self.pk_field_names = {}
|
|
for lh_field, rh_field in self.source_field.related_fields:
|
|
core_filter_key = '%s__%s' % (self.query_field_name, rh_field.name)
|
|
self.core_filters[core_filter_key] = getattr(instance, rh_field.attname)
|
|
self.pk_field_names[lh_field.name] = rh_field.name
|
|
|
|
self.related_val = self.source_field.get_foreign_related_value(instance)
|
|
if None in self.related_val:
|
|
raise ValueError('"%r" needs to have a value for field "%s" before '
|
|
'this many-to-many relationship can be used.' %
|
|
(instance, self.pk_field_names[self.source_field_name]))
|
|
# Even if this relation is not to pk, we require still pk value.
|
|
# The wish is that the instance has been already saved to DB,
|
|
# although having a pk value isn't a guarantee of that.
|
|
if instance.pk is None:
|
|
raise ValueError("%r instance needs to have a primary key value before "
|
|
"a many-to-many relationship can be used." %
|
|
instance.__class__.__name__)
|
|
|
|
def __call__(self, *, manager):
|
|
manager = getattr(self.model, manager)
|
|
manager_class = create_forward_many_to_many_manager(manager.__class__, rel, reverse)
|
|
return manager_class(instance=self.instance)
|
|
do_not_call_in_templates = True
|
|
|
|
def _build_remove_filters(self, removed_vals):
|
|
filters = Q(**{self.source_field_name: self.related_val})
|
|
# No need to add a subquery condition if removed_vals is a QuerySet without
|
|
# filters.
|
|
removed_vals_filters = (not isinstance(removed_vals, QuerySet) or
|
|
removed_vals._has_filters())
|
|
if removed_vals_filters:
|
|
filters &= Q(**{'%s__in' % self.target_field_name: removed_vals})
|
|
if self.symmetrical:
|
|
symmetrical_filters = Q(**{self.target_field_name: self.related_val})
|
|
if removed_vals_filters:
|
|
symmetrical_filters &= Q(
|
|
**{'%s__in' % self.source_field_name: removed_vals})
|
|
filters |= symmetrical_filters
|
|
return filters
|
|
|
|
def _apply_rel_filters(self, queryset):
|
|
"""
|
|
Filter the queryset for the instance this manager is bound to.
|
|
"""
|
|
queryset._add_hints(instance=self.instance)
|
|
if self._db:
|
|
queryset = queryset.using(self._db)
|
|
return queryset._next_is_sticky().filter(**self.core_filters)
|
|
|
|
def _remove_prefetched_objects(self):
|
|
try:
|
|
self.instance._prefetched_objects_cache.pop(self.prefetch_cache_name)
|
|
except (AttributeError, KeyError):
|
|
pass # nothing to clear from cache
|
|
|
|
def get_queryset(self):
|
|
try:
|
|
return self.instance._prefetched_objects_cache[self.prefetch_cache_name]
|
|
except (AttributeError, KeyError):
|
|
queryset = super().get_queryset()
|
|
return self._apply_rel_filters(queryset)
|
|
|
|
def get_prefetch_queryset(self, instances, queryset=None):
|
|
if queryset is None:
|
|
queryset = super().get_queryset()
|
|
|
|
queryset._add_hints(instance=instances[0])
|
|
queryset = queryset.using(queryset._db or self._db)
|
|
|
|
query = {'%s__in' % self.query_field_name: instances}
|
|
queryset = queryset._next_is_sticky().filter(**query)
|
|
|
|
# M2M: need to annotate the query in order to get the primary model
|
|
# that the secondary model was actually related to. We know that
|
|
# there will already be a join on the join table, so we can just add
|
|
# the select.
|
|
|
|
# For non-autocreated 'through' models, can't assume we are
|
|
# dealing with PK values.
|
|
fk = self.through._meta.get_field(self.source_field_name)
|
|
join_table = fk.model._meta.db_table
|
|
connection = connections[queryset.db]
|
|
qn = connection.ops.quote_name
|
|
queryset = queryset.extra(select={
|
|
'_prefetch_related_val_%s' % f.attname:
|
|
'%s.%s' % (qn(join_table), qn(f.column)) for f in fk.local_related_fields})
|
|
return (
|
|
queryset,
|
|
lambda result: tuple(
|
|
getattr(result, '_prefetch_related_val_%s' % f.attname)
|
|
for f in fk.local_related_fields
|
|
),
|
|
lambda inst: tuple(
|
|
f.get_db_prep_value(getattr(inst, f.attname), connection)
|
|
for f in fk.foreign_related_fields
|
|
),
|
|
False,
|
|
self.prefetch_cache_name,
|
|
)
|
|
|
|
def add(self, *objs):
|
|
if not rel.through._meta.auto_created:
|
|
opts = self.through._meta
|
|
raise AttributeError(
|
|
"Cannot use add() on a ManyToManyField which specifies an "
|
|
"intermediary model. Use %s.%s's Manager instead." %
|
|
(opts.app_label, opts.object_name)
|
|
)
|
|
self._remove_prefetched_objects()
|
|
db = router.db_for_write(self.through, instance=self.instance)
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
self._add_items(self.source_field_name, self.target_field_name, *objs)
|
|
|
|
# If this is a symmetrical m2m relation to self, add the mirror entry in the m2m table
|
|
if self.symmetrical:
|
|
self._add_items(self.target_field_name, self.source_field_name, *objs)
|
|
add.alters_data = True
|
|
|
|
def remove(self, *objs):
|
|
if not rel.through._meta.auto_created:
|
|
opts = self.through._meta
|
|
raise AttributeError(
|
|
"Cannot use remove() on a ManyToManyField which specifies "
|
|
"an intermediary model. Use %s.%s's Manager instead." %
|
|
(opts.app_label, opts.object_name)
|
|
)
|
|
self._remove_prefetched_objects()
|
|
self._remove_items(self.source_field_name, self.target_field_name, *objs)
|
|
remove.alters_data = True
|
|
|
|
def clear(self):
|
|
db = router.db_for_write(self.through, instance=self.instance)
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action="pre_clear",
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=None, using=db,
|
|
)
|
|
self._remove_prefetched_objects()
|
|
filters = self._build_remove_filters(super().get_queryset().using(db))
|
|
self.through._default_manager.using(db).filter(filters).delete()
|
|
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action="post_clear",
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=None, using=db,
|
|
)
|
|
clear.alters_data = True
|
|
|
|
def set(self, objs, *, clear=False):
|
|
if not rel.through._meta.auto_created:
|
|
opts = self.through._meta
|
|
raise AttributeError(
|
|
"Cannot set values on a ManyToManyField which specifies an "
|
|
"intermediary model. Use %s.%s's Manager instead." %
|
|
(opts.app_label, opts.object_name)
|
|
)
|
|
|
|
# Force evaluation of `objs` in case it's a queryset whose value
|
|
# could be affected by `manager.clear()`. Refs #19816.
|
|
objs = tuple(objs)
|
|
|
|
db = router.db_for_write(self.through, instance=self.instance)
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
if clear:
|
|
self.clear()
|
|
self.add(*objs)
|
|
else:
|
|
old_ids = set(self.using(db).values_list(self.target_field.target_field.attname, flat=True))
|
|
|
|
new_objs = []
|
|
for obj in objs:
|
|
fk_val = (
|
|
self.target_field.get_foreign_related_value(obj)[0]
|
|
if isinstance(obj, self.model) else obj
|
|
)
|
|
if fk_val in old_ids:
|
|
old_ids.remove(fk_val)
|
|
else:
|
|
new_objs.append(obj)
|
|
|
|
self.remove(*old_ids)
|
|
self.add(*new_objs)
|
|
set.alters_data = True
|
|
|
|
def create(self, **kwargs):
|
|
# This check needs to be done here, since we can't later remove this
|
|
# from the method lookup table, as we do with add and remove.
|
|
if not self.through._meta.auto_created:
|
|
opts = self.through._meta
|
|
raise AttributeError(
|
|
"Cannot use create() on a ManyToManyField which specifies "
|
|
"an intermediary model. Use %s.%s's Manager instead." %
|
|
(opts.app_label, opts.object_name)
|
|
)
|
|
db = router.db_for_write(self.instance.__class__, instance=self.instance)
|
|
new_obj = super(ManyRelatedManager, self.db_manager(db)).create(**kwargs)
|
|
self.add(new_obj)
|
|
return new_obj
|
|
create.alters_data = True
|
|
|
|
def get_or_create(self, **kwargs):
|
|
db = router.db_for_write(self.instance.__class__, instance=self.instance)
|
|
obj, created = super(ManyRelatedManager, self.db_manager(db)).get_or_create(**kwargs)
|
|
# We only need to add() if created because if we got an object back
|
|
# from get() then the relationship already exists.
|
|
if created:
|
|
self.add(obj)
|
|
return obj, created
|
|
get_or_create.alters_data = True
|
|
|
|
def update_or_create(self, **kwargs):
|
|
db = router.db_for_write(self.instance.__class__, instance=self.instance)
|
|
obj, created = super(ManyRelatedManager, self.db_manager(db)).update_or_create(**kwargs)
|
|
# We only need to add() if created because if we got an object back
|
|
# from get() then the relationship already exists.
|
|
if created:
|
|
self.add(obj)
|
|
return obj, created
|
|
update_or_create.alters_data = True
|
|
|
|
def _add_items(self, source_field_name, target_field_name, *objs):
|
|
# source_field_name: the PK fieldname in join table for the source object
|
|
# target_field_name: the PK fieldname in join table for the target object
|
|
# *objs - objects to add. Either object instances, or primary keys of object instances.
|
|
|
|
# If there aren't any objects, there is nothing to do.
|
|
from django.db.models import Model
|
|
if objs:
|
|
new_ids = set()
|
|
for obj in objs:
|
|
if isinstance(obj, self.model):
|
|
if not router.allow_relation(obj, self.instance):
|
|
raise ValueError(
|
|
'Cannot add "%r": instance is on database "%s", value is on database "%s"' %
|
|
(obj, self.instance._state.db, obj._state.db)
|
|
)
|
|
fk_val = self.through._meta.get_field(
|
|
target_field_name).get_foreign_related_value(obj)[0]
|
|
if fk_val is None:
|
|
raise ValueError(
|
|
'Cannot add "%r": the value for field "%s" is None' %
|
|
(obj, target_field_name)
|
|
)
|
|
new_ids.add(fk_val)
|
|
elif isinstance(obj, Model):
|
|
raise TypeError(
|
|
"'%s' instance expected, got %r" %
|
|
(self.model._meta.object_name, obj)
|
|
)
|
|
else:
|
|
new_ids.add(obj)
|
|
|
|
db = router.db_for_write(self.through, instance=self.instance)
|
|
vals = (self.through._default_manager.using(db)
|
|
.values_list(target_field_name, flat=True)
|
|
.filter(**{
|
|
source_field_name: self.related_val[0],
|
|
'%s__in' % target_field_name: new_ids,
|
|
}))
|
|
new_ids = new_ids - set(vals)
|
|
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
if self.reverse or source_field_name == self.source_field_name:
|
|
# Don't send the signal when we are inserting the
|
|
# duplicate data row for symmetrical reverse entries.
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action='pre_add',
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=new_ids, using=db,
|
|
)
|
|
|
|
# Add the ones that aren't there already
|
|
self.through._default_manager.using(db).bulk_create([
|
|
self.through(**{
|
|
'%s_id' % source_field_name: self.related_val[0],
|
|
'%s_id' % target_field_name: obj_id,
|
|
})
|
|
for obj_id in new_ids
|
|
])
|
|
|
|
if self.reverse or source_field_name == self.source_field_name:
|
|
# Don't send the signal when we are inserting the
|
|
# duplicate data row for symmetrical reverse entries.
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action='post_add',
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=new_ids, using=db,
|
|
)
|
|
|
|
def _remove_items(self, source_field_name, target_field_name, *objs):
|
|
# source_field_name: the PK colname in join table for the source object
|
|
# target_field_name: the PK colname in join table for the target object
|
|
# *objs - objects to remove
|
|
if not objs:
|
|
return
|
|
|
|
# Check that all the objects are of the right type
|
|
old_ids = set()
|
|
for obj in objs:
|
|
if isinstance(obj, self.model):
|
|
fk_val = self.target_field.get_foreign_related_value(obj)[0]
|
|
old_ids.add(fk_val)
|
|
else:
|
|
old_ids.add(obj)
|
|
|
|
db = router.db_for_write(self.through, instance=self.instance)
|
|
with transaction.atomic(using=db, savepoint=False):
|
|
# Send a signal to the other end if need be.
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action="pre_remove",
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=old_ids, using=db,
|
|
)
|
|
target_model_qs = super().get_queryset()
|
|
if target_model_qs._has_filters():
|
|
old_vals = target_model_qs.using(db).filter(**{
|
|
'%s__in' % self.target_field.target_field.attname: old_ids})
|
|
else:
|
|
old_vals = old_ids
|
|
filters = self._build_remove_filters(old_vals)
|
|
self.through._default_manager.using(db).filter(filters).delete()
|
|
|
|
signals.m2m_changed.send(
|
|
sender=self.through, action="post_remove",
|
|
instance=self.instance, reverse=self.reverse,
|
|
model=self.model, pk_set=old_ids, using=db,
|
|
)
|
|
|
|
return ManyRelatedManager
|