django1/django/db/models/fields/reverse_related.py

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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 __future__ import unicode_literals
import warnings
from django.core import exceptions
from django.utils.deprecation import RemovedInDjango20Warning
from django.utils.encoding import smart_text
from django.utils.functional import cached_property
from . import BLANK_CHOICE_DASH
class ForeignObjectRel(object):
"""
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
@property
def to(self):
warnings.warn(
"Usage of ForeignObjectRel.to attribute has been deprecated. "
"Use the model attribute instead.",
RemovedInDjango20Warning, 2)
return self.model
@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, returns 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_prep_lookup(self, lookup_name, value):
return self.field.get_prep_lookup(lookup_name, value)
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,
limit_to_currently_related=False):
"""
Return choices with a default blank choices included, for use as
SelectField choices for this field.
Analog of django.db.models.fields.Field.get_choices(), provided
initially for utilization by RelatedFieldListFilter.
"""
first_choice = blank_choice if include_blank else []
queryset = self.related_model._default_manager.all()
if limit_to_currently_related:
queryset = queryset.complex_filter(
{'%s__isnull' % self.related_model._meta.model_name: False}
)
lst = [(x._get_pk_val(), smart_text(x)) for x in queryset]
return first_choice + lst
def get_db_prep_lookup(self, lookup_type, value, connection, prepared=False):
# Defer to the actual field definition for db prep
return self.field.get_db_prep_lookup(lookup_type, value, connection=connection, prepared=prepared)
def is_hidden(self):
"Should the related object be hidden?"
return self.related_name is not None 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 lower-cased 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
if opts.default_related_name:
return opts.default_related_name % {
'model_name': opts.model_name.lower(),
'app_label': opts.app_label.lower(),
}
return opts.model_name + ('_set' if self.multiple else '')
def get_cache_name(self):
return "_%s_cache" % self.get_accessor_name()
def get_path_info(self):
return self.field.get_reverse_path_info()
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(ManyToOneRel, self).__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(OneToOneRel, self).__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(ManyToManyRel, self).__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]