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- """
- "Rel objects" for related fields.
-
- "Rel objects" (for lack of a better name) carry information about the relation
- modeled by a related field and provide some utility functions. They're stored
- in the ``remote_field`` attribute of the field.
-
- They also act as reverse fields for the purposes of the Meta API because
- they're the closest concept currently available.
- """
-
- from django.core import exceptions
- from django.utils.functional import cached_property
-
- from . import BLANK_CHOICE_DASH
- from .mixins import FieldCacheMixin
-
-
- class ForeignObjectRel(FieldCacheMixin):
- """
- Used by ForeignObject to store information about the relation.
-
- ``_meta.get_fields()`` returns this class to provide access to the field
- flags for the reverse relation.
- """
-
- # Field flags
- auto_created = True
- concrete = False
- editable = False
- is_relation = True
-
- # Reverse relations are always nullable (Django can't enforce that a
- # foreign key on the related model points to this model).
- null = True
-
- def __init__(self, field, to, related_name=None, related_query_name=None,
- limit_choices_to=None, parent_link=False, on_delete=None):
- self.field = field
- self.model = to
- self.related_name = related_name
- self.related_query_name = related_query_name
- self.limit_choices_to = {} if limit_choices_to is None else limit_choices_to
- self.parent_link = parent_link
- self.on_delete = on_delete
-
- self.symmetrical = False
- self.multiple = True
-
- # Some of the following cached_properties can't be initialized in
- # __init__ as the field doesn't have its model yet. Calling these methods
- # before field.contribute_to_class() has been called will result in
- # AttributeError
- @cached_property
- def hidden(self):
- return self.is_hidden()
-
- @cached_property
- def name(self):
- return self.field.related_query_name()
-
- @property
- def remote_field(self):
- return self.field
-
- @property
- def target_field(self):
- """
- When filtering against this relation, return the field on the remote
- model against which the filtering should happen.
- """
- target_fields = self.get_path_info()[-1].target_fields
- if len(target_fields) > 1:
- raise exceptions.FieldError("Can't use target_field for multicolumn relations.")
- return target_fields[0]
-
- @cached_property
- def related_model(self):
- if not self.field.model:
- raise AttributeError(
- "This property can't be accessed before self.field.contribute_to_class has been called.")
- return self.field.model
-
- @cached_property
- def many_to_many(self):
- return self.field.many_to_many
-
- @cached_property
- def many_to_one(self):
- return self.field.one_to_many
-
- @cached_property
- def one_to_many(self):
- return self.field.many_to_one
-
- @cached_property
- def one_to_one(self):
- return self.field.one_to_one
-
- def get_lookup(self, lookup_name):
- return self.field.get_lookup(lookup_name)
-
- def get_internal_type(self):
- return self.field.get_internal_type()
-
- @property
- def db_type(self):
- return self.field.db_type
-
- def __repr__(self):
- return '<%s: %s.%s>' % (
- type(self).__name__,
- self.related_model._meta.app_label,
- self.related_model._meta.model_name,
- )
-
- def get_choices(self, include_blank=True, blank_choice=BLANK_CHOICE_DASH, ordering=()):
- """
- Return choices with a default blank choices included, for use
- as <select> choices for this field.
-
- Analog of django.db.models.fields.Field.get_choices(), provided
- initially for utilization by RelatedFieldListFilter.
- """
- qs = self.related_model._default_manager.all()
- if ordering:
- qs = qs.order_by(*ordering)
- return (blank_choice if include_blank else []) + [
- (x.pk, str(x)) for x in qs
- ]
-
- def is_hidden(self):
- """Should the related object be hidden?"""
- return bool(self.related_name) and self.related_name[-1] == '+'
-
- def get_joining_columns(self):
- return self.field.get_reverse_joining_columns()
-
- def get_extra_restriction(self, where_class, alias, related_alias):
- return self.field.get_extra_restriction(where_class, related_alias, alias)
-
- def set_field_name(self):
- """
- Set the related field's name, this is not available until later stages
- of app loading, so set_field_name is called from
- set_attributes_from_rel()
- """
- # By default foreign object doesn't relate to any remote field (for
- # example custom multicolumn joins currently have no remote field).
- self.field_name = None
-
- def get_accessor_name(self, model=None):
- # This method encapsulates the logic that decides what name to give an
- # accessor descriptor that retrieves related many-to-one or
- # many-to-many objects. It uses the lowercased object_name + "_set",
- # but this can be overridden with the "related_name" option. Due to
- # backwards compatibility ModelForms need to be able to provide an
- # alternate model. See BaseInlineFormSet.get_default_prefix().
- opts = model._meta if model else self.related_model._meta
- model = model or self.related_model
- if self.multiple:
- # If this is a symmetrical m2m relation on self, there is no reverse accessor.
- if self.symmetrical and model == self.model:
- return None
- if self.related_name:
- return self.related_name
- return opts.model_name + ('_set' if self.multiple else '')
-
- def get_path_info(self, filtered_relation=None):
- return self.field.get_reverse_path_info(filtered_relation)
-
- def get_cache_name(self):
- """
- Return the name of the cache key to use for storing an instance of the
- forward model on the reverse model.
- """
- return self.get_accessor_name()
-
-
- class ManyToOneRel(ForeignObjectRel):
- """
- Used by the ForeignKey field to store information about the relation.
-
- ``_meta.get_fields()`` returns this class to provide access to the field
- flags for the reverse relation.
-
- Note: Because we somewhat abuse the Rel objects by using them as reverse
- fields we get the funny situation where
- ``ManyToOneRel.many_to_one == False`` and
- ``ManyToOneRel.one_to_many == True``. This is unfortunate but the actual
- ManyToOneRel class is a private API and there is work underway to turn
- reverse relations into actual fields.
- """
-
- def __init__(self, field, to, field_name, related_name=None, related_query_name=None,
- limit_choices_to=None, parent_link=False, on_delete=None):
- super().__init__(
- field, to,
- related_name=related_name,
- related_query_name=related_query_name,
- limit_choices_to=limit_choices_to,
- parent_link=parent_link,
- on_delete=on_delete,
- )
-
- self.field_name = field_name
-
- def __getstate__(self):
- state = self.__dict__.copy()
- state.pop('related_model', None)
- return state
-
- def get_related_field(self):
- """
- Return the Field in the 'to' object to which this relationship is tied.
- """
- field = self.model._meta.get_field(self.field_name)
- if not field.concrete:
- raise exceptions.FieldDoesNotExist("No related field named '%s'" % self.field_name)
- return field
-
- def set_field_name(self):
- self.field_name = self.field_name or self.model._meta.pk.name
-
-
- class OneToOneRel(ManyToOneRel):
- """
- Used by OneToOneField to store information about the relation.
-
- ``_meta.get_fields()`` returns this class to provide access to the field
- flags for the reverse relation.
- """
-
- def __init__(self, field, to, field_name, related_name=None, related_query_name=None,
- limit_choices_to=None, parent_link=False, on_delete=None):
- super().__init__(
- field, to, field_name,
- related_name=related_name,
- related_query_name=related_query_name,
- limit_choices_to=limit_choices_to,
- parent_link=parent_link,
- on_delete=on_delete,
- )
-
- self.multiple = False
-
-
- class ManyToManyRel(ForeignObjectRel):
- """
- Used by ManyToManyField to store information about the relation.
-
- ``_meta.get_fields()`` returns this class to provide access to the field
- flags for the reverse relation.
- """
-
- def __init__(self, field, to, related_name=None, related_query_name=None,
- limit_choices_to=None, symmetrical=True, through=None,
- through_fields=None, db_constraint=True):
- super().__init__(
- field, to,
- related_name=related_name,
- related_query_name=related_query_name,
- limit_choices_to=limit_choices_to,
- )
-
- if through and not db_constraint:
- raise ValueError("Can't supply a through model and db_constraint=False")
- self.through = through
-
- if through_fields and not through:
- raise ValueError("Cannot specify through_fields without a through model")
- self.through_fields = through_fields
-
- self.symmetrical = symmetrical
- self.db_constraint = db_constraint
-
- def get_related_field(self):
- """
- Return the field in the 'to' object to which this relationship is tied.
- Provided for symmetry with ManyToOneRel.
- """
- opts = self.through._meta
- if self.through_fields:
- field = opts.get_field(self.through_fields[0])
- else:
- for field in opts.fields:
- rel = getattr(field, 'remote_field', None)
- if rel and rel.model == self.model:
- break
- return field.foreign_related_fields[0]
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