Source code
import functools
import inspect
from functools import partial
from django import forms
from django.apps import apps
from django.conf import SettingsReference, settings
from django.core import checks, exceptions
from django.db import connection, connections, router
from django.db.backends import utils
from django.db.models import NOT_PROVIDED, Q
from django.db.models.constants import LOOKUP_SEP
from django.db.models.deletion import (
CASCADE,
DB_CASCADE,
DB_SET_DEFAULT,
DB_SET_NULL,
DO_NOTHING,
SET_DEFAULT,
SET_NULL,
DatabaseOnDelete,
)
from django.db.models.query_utils import PathInfo
from django.db.models.utils import make_model_tuple
from django.utils.functional import cached_property
from django.utils.translation import gettext_lazy as _
from . import Field
from .mixins import FieldCacheMixin
from .related_descriptors import (
ForeignKeyDeferredAttribute,
ForwardManyToOneDescriptor,
ForwardOneToOneDescriptor,
ManyToManyDescriptor,
ReverseManyToOneDescriptor,
ReverseOneToOneDescriptor,
)
from .related_lookups import (
RelatedExact,
RelatedGreaterThan,
RelatedGreaterThanOrEqual,
RelatedIn,
RelatedIsNull,
RelatedLessThan,
RelatedLessThanOrEqual,
)
from .reverse_related import ForeignObjectRel, ManyToManyRel, ManyToOneRel, OneToOneRel
class ForeignObject(RelatedField):
"""
Abstraction of the ForeignKey relation to support multi-column relations.
"""
# Field flags
many_to_many = False
many_to_one = True
one_to_many = False
one_to_one = False
requires_unique_target = True
related_accessor_class = ReverseManyToOneDescriptor
forward_related_accessor_class = ForwardManyToOneDescriptor
rel_class = ForeignObjectRel
def __init__(
self,
to,
on_delete,
from_fields,
to_fields,
rel=None,
related_name=None,
related_query_name=None,
limit_choices_to=None,
parent_link=False,
swappable=True,
**kwargs,
):
if rel is None:
rel = self.rel_class(
self,
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,
)
super().__init__(
rel=rel,
related_name=related_name,
related_query_name=related_query_name,
limit_choices_to=limit_choices_to,
**kwargs,
)
self.from_fields = from_fields
self.to_fields = to_fields
self.swappable = swappable
def __copy__(self):
obj = super().__copy__()
# Remove any cached PathInfo values.
obj.__dict__.pop("path_infos", None)
obj.__dict__.pop("reverse_path_infos", None)
return obj
@property
def non_db_attrs(self):
if isinstance(self.remote_field.on_delete, DatabaseOnDelete):
# Database-level on_delete options are part of the column
# definition.
return super().non_db_attrs
return super().non_db_attrs + ("on_delete",)
def check(self, **kwargs):
return [
*super().check(**kwargs),
*self._check_to_fields_exist(),
*self._check_to_fields_composite_pk(),
*self._check_unique_target(),
]
def _check_to_fields_exist(self):
# Skip nonexistent models.
if isinstance(self.remote_field.model, str):
return []
errors = []
for to_field in self.to_fields:
if to_field:
try:
self.remote_field.model._meta.get_field(to_field)
except exceptions.FieldDoesNotExist:
errors.append(
checks.Error(
"The to_field '%s' doesn't exist on the related "
"model '%s'."
% (to_field, self.remote_field.model._meta.label),
obj=self,
id="fields.E312",
)
)
return errors
def _check_to_fields_composite_pk(self):
from django.db.models.fields.composite import CompositePrimaryKey
# Skip nonexistent models.
if isinstance(self.remote_field.model, str):
return []
errors = []
for to_field in self.to_fields:
try:
field = (
self.remote_field.model._meta.pk
if to_field is None
else self.remote_field.model._meta.get_field(to_field)
)
except exceptions.FieldDoesNotExist:
pass
else:
if isinstance(field, CompositePrimaryKey):
errors.append(
checks.Error(
"Field defines a relation involving model "
f"{self.remote_field.model._meta.object_name!r} which has "
"a CompositePrimaryKey and such relations are not "
"supported.",
obj=self,
id="fields.E347",
)
)
return errors
def _check_unique_target(self):
rel_is_string = isinstance(self.remote_field.model, str)
if rel_is_string or not self.requires_unique_target:
return []
try:
self.foreign_related_fields
except exceptions.FieldDoesNotExist:
return []
if not self.foreign_related_fields:
return []
has_unique_constraint = any(
rel_field.unique for rel_field in self.foreign_related_fields
)
if not has_unique_constraint:
foreign_fields = {f.name for f in self.foreign_related_fields}
remote_opts = self.remote_field.model._meta
has_unique_constraint = (
any(
frozenset(ut) <= foreign_fields
for ut in remote_opts.unique_together
)
or any(
frozenset(uc.fields) <= foreign_fields
for uc in remote_opts.total_unique_constraints
)
# If the model defines a composite primary key and the foreign
# key refers to it, the target is unique.
or (
frozenset(field.name for field in remote_opts.pk_fields)
== foreign_fields
)
)
if not has_unique_constraint:
if len(self.foreign_related_fields) > 1:
field_combination = ", ".join(
f"'{rel_field.name}'" for rel_field in self.foreign_related_fields
)
model_name = self.remote_field.model.__name__
return [
checks.Error(
f"No subset of the fields {field_combination} on model "
f"'{model_name}' is unique.",
hint=(
"Mark a single field as unique=True or add a set of "
"fields to a unique constraint (via unique_together "
"or a UniqueConstraint (without condition) in the "
"model Meta.constraints)."
),
obj=self,
id="fields.E310",
)
]
else:
field_name = self.foreign_related_fields[0].name
model_name = self.remote_field.model.__name__
return [
checks.Error(
f"'{model_name}.{field_name}' must be unique because it is "
"referenced by a foreign key.",
hint=(
"Add unique=True to this field or add a "
"UniqueConstraint (without condition) in the model "
"Meta.constraints."
),
obj=self,
id="fields.E311",
)
]
return []
def deconstruct(self):
name, path, args, kwargs = super().deconstruct()
kwargs["on_delete"] = self.remote_field.on_delete
kwargs["from_fields"] = self.from_fields
kwargs["to_fields"] = self.to_fields
if self.remote_field.parent_link:
kwargs["parent_link"] = self.remote_field.parent_link
if isinstance(self.remote_field.model, str):
if "." in self.remote_field.model:
app_label, model_name = self.remote_field.model.split(".")
kwargs["to"] = "%s.%s" % (app_label, model_name.lower())
else:
kwargs["to"] = self.remote_field.model.lower()
else:
kwargs["to"] = self.remote_field.model._meta.label_lower
# If swappable is True, then see if we're actually pointing to the
# target of a swap.
swappable_setting = self.swappable_setting
if swappable_setting is not None:
# If it's already a settings reference, error
if hasattr(kwargs["to"], "setting_name"):
if kwargs["to"].setting_name != swappable_setting:
raise ValueError(
"Cannot deconstruct a ForeignKey pointing to a model "
"that is swapped in place of more than one model (%s and %s)"
% (kwargs["to"].setting_name, swappable_setting)
)
# Set it
kwargs["to"] = SettingsReference(
kwargs["to"],
swappable_setting,
)
return name, path, args, kwargs
def resolve_related_fields(self):
if not self.from_fields or len(self.from_fields) != len(self.to_fields):
raise ValueError(
"Foreign Object from and to fields must be the same non-zero length"
)
if isinstance(self.remote_field.model, str):
raise ValueError(
"Related model %r cannot be resolved" % self.remote_field.model
)
related_fields = []
for from_field_name, to_field_name in zip(self.from_fields, self.to_fields):
from_field = (
self
if from_field_name == RECURSIVE_RELATIONSHIP_CONSTANT
else self.opts.get_field(from_field_name)
)
to_field = (
self.remote_field.model._meta.pk
if to_field_name is None
else self.remote_field.model._meta.get_field(to_field_name)
)
related_fields.append((from_field, to_field))
return related_fields
@cached_property
def related_fields(self):
return self.resolve_related_fields()
@cached_property
def reverse_related_fields(self):
return [(rhs_field, lhs_field) for lhs_field, rhs_field in self.related_fields]
@cached_property
def local_related_fields(self):
return tuple(lhs_field for lhs_field, rhs_field in self.related_fields)
@cached_property
def foreign_related_fields(self):
return tuple(
rhs_field for lhs_field, rhs_field in self.related_fields if rhs_field
)
def get_local_related_value(self, instance):
return self.get_instance_value_for_fields(instance, self.local_related_fields)
def get_foreign_related_value(self, instance):
return self.get_instance_value_for_fields(instance, self.foreign_related_fields)
@staticmethod
def get_instance_value_for_fields(instance, fields):
ret = []
opts = instance._meta
for field in fields:
# Gotcha: in some cases (like fixture loading) a model can have
# different values in parent_ptr_id and parent's id. So, use
# instance.pk (that is, parent_ptr_id) when asked for instance.id.
if field.primary_key:
possible_parent_link = opts.get_ancestor_link(field.model)
if (
not possible_parent_link
or possible_parent_link.primary_key
or possible_parent_link.model._meta.abstract
):
ret.append(instance.pk)
continue
ret.append(getattr(instance, field.attname))
return tuple(ret)
def get_attname_column(self):
attname, column = super().get_attname_column()
return attname, None
def get_joining_fields(self, reverse_join=False):
return tuple(
self.reverse_related_fields if reverse_join else self.related_fields
)
def get_reverse_joining_fields(self):
return self.get_joining_fields(reverse_join=True)
def get_extra_descriptor_filter(self, instance):
"""
Return an extra filter condition for related object fetching when
user does 'instance.fieldname', that is the extra filter is used in
the descriptor of the field.
The filter should be either a dict usable in .filter(**kwargs) call or
a Q-object. The condition will be ANDed together with the relation's
joining columns.
A parallel method is get_extra_restriction() which is used in
JOIN and subquery conditions.
"""
return {}
def get_extra_restriction(self, alias, related_alias):
"""
Return a pair condition used for joining and subquery pushdown. The
condition is something that responds to as_sql(compiler, connection)
method.
Note that currently referring both the 'alias' and 'related_alias'
will not work in some conditions, like subquery pushdown.
A parallel method is get_extra_descriptor_filter() which is used in
instance.fieldname related object fetching.
"""
return None
def get_path_info(self, filtered_relation=None):
"""Get path from this field to the related model."""
opts = self.remote_field.model._meta
from_opts = self.model._meta
return [
PathInfo(
from_opts=from_opts,
to_opts=opts,
target_fields=self.foreign_related_fields,
join_field=self,
m2m=False,
direct=True,
filtered_relation=filtered_relation,
)
]
@cached_property
def path_infos(self):
return self.get_path_info()
def get_reverse_path_info(self, filtered_relation=None):
"""Get path from the related model to this field's model."""
remaining_steps = 3
while remaining_steps > 0:
remaining_steps -= 1
opts = self.model._meta
from_opts = self.remote_field.model._meta
return [
PathInfo(
from_opts=from_opts,
to_opts=opts,
target_fields=(opts.pk,),
join_field=self.remote_field,
m2m=not self.unique,
direct=False,
filtered_relation=filtered_relation,
)
]
@cached_property
def reverse_path_infos(self):
return self.get_reverse_path_info()
@classmethod
@functools.cache
def get_class_lookups(cls):
bases = inspect.getmro(cls)
bases = bases[: bases.index(ForeignObject) + 1]
class_lookups = [parent.__dict__.get("class_lookups", {}) for parent in bases]
return cls.merge_dicts(class_lookups)
def contribute_to_class(self, cls, name, private_only=False, **kwargs):
super().contribute_to_class(cls, name, private_only=private_only, **kwargs)
setattr(cls, self.name, self.forward_related_accessor_class(self))
def contribute_to_related_class(self, cls, related):
# Internal FK's - i.e., those with a related name ending with '+' -
# and swapped models don't get a related descriptor.
if not self.remote_field.hidden and not related.related_model._meta.swapped:
setattr(
cls._meta.concrete_model,
related.accessor_name,
self.related_accessor_class(related),
)
# While 'limit_choices_to' might be a callable, simply pass
# it along for later - this is too early because it's still
# model load time.
if self.remote_field.limit_choices_to:
cls._meta.related_fkey_lookups.append(
self.remote_field.limit_choices_to
)