Added generic foreign key support to Django. Much thanks to Ian Holsman and
Luke Plant -- most of this code is theirs. Documentation is to follow; for now see the example/unit test. Fixes #529. git-svn-id: http://code.djangoproject.com/svn/django/trunk@3134 bcc190cf-cafb-0310-a4f2-bffc1f526a37
This commit is contained in:
Jacob Kaplan-Moss
parent
174e334d92
commit
bca5327b21
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@ -211,11 +211,14 @@ def _get_sql_for_pending_references(klass, pending_references):
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def _get_many_to_many_sql_for_model(klass):
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from django.db import backend, get_creation_module
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from django.db.models import GenericRel
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data_types = get_creation_module().DATA_TYPES
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opts = klass._meta
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final_output = []
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for f in opts.many_to_many:
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if not isinstance(f.rel, GenericRel):
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table_output = [style.SQL_KEYWORD('CREATE TABLE') + ' ' + \
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style.SQL_TABLE(backend.quote_name(f.m2m_db_table())) + ' (']
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table_output.append(' %s %s %s,' % \
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@ -8,6 +8,7 @@ from django.db.models.manager import Manager
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from django.db.models.base import Model, AdminOptions
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from django.db.models.fields import *
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from django.db.models.fields.related import ForeignKey, OneToOneField, ManyToManyField, ManyToOneRel, ManyToManyRel, OneToOneRel, TABULAR, STACKED
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from django.db.models.fields.generic import GenericRelation, GenericRel, GenericForeignKey
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from django.db.models import signals
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from django.utils.functional import curry
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from django.utils.text import capfirst
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@ -0,0 +1,259 @@
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"""
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Classes allowing "generic" relations through ContentType and object-id fields.
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"""
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from django import forms
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from django.core.exceptions import ObjectDoesNotExist
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from django.db import backend
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from django.db.models import signals
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from django.db.models.fields.related import RelatedField, Field, ManyToManyRel
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from django.db.models.loading import get_model
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from django.dispatch import dispatcher
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from django.utils.functional import curry
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class GenericForeignKey(object):
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"""
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Provides a generic relation to any object through content-type/object-id
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fields.
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"""
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def __init__(self, ct_field="content_type", fk_field="object_id"):
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self.ct_field = ct_field
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self.fk_field = fk_field
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def contribute_to_class(self, cls, name):
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# Make sure the fields exist (these raise FieldDoesNotExist,
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# which is a fine error to raise here)
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self.name = name
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self.model = cls
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self.cache_attr = "_%s_cache" % name
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# For some reason I don't totally understand, using weakrefs here doesn't work.
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dispatcher.connect(self.instance_pre_init, signal=signals.pre_init, sender=cls, weak=False)
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# Connect myself as the descriptor for this field
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setattr(cls, name, self)
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def instance_pre_init(self, signal, sender, args, kwargs):
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# Handle initalizing an object with the generic FK instaed of
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# content-type/object-id fields.
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if kwargs.has_key(self.name):
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value = kwargs.pop(self.name)
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kwargs[self.ct_field] = self.get_content_type(value)
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kwargs[self.fk_field] = value._get_pk_val()
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def get_content_type(self, obj):
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# Convenience function using get_model avoids a circular import when using this model
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ContentType = get_model("contenttypes", "contenttype")
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return ContentType.objects.get_for_model(obj)
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def __get__(self, instance, instance_type=None):
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if instance is None:
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raise AttributeError, "%s must be accessed via instance" % self.name
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try:
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return getattr(instance, self.cache_attr)
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except AttributeError:
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rel_obj = None
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ct = getattr(instance, self.ct_field)
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if ct:
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try:
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rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))
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except ObjectDoesNotExist:
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pass
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setattr(instance, self.cache_attr, rel_obj)
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return rel_obj
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def __set__(self, instance, value):
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if instance is None:
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raise AttributeError, "%s must be accessed via instance" % self.related.opts.object_name
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ct = None
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fk = None
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if value is not None:
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ct = self.get_content_type(value)
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fk = value._get_pk_val()
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setattr(instance, self.ct_field, ct)
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setattr(instance, self.fk_field, fk)
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setattr(instance, self.cache_attr, value)
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class GenericRelation(RelatedField, Field):
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"""Provides an accessor to generic related objects (i.e. comments)"""
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def __init__(self, to, **kwargs):
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kwargs['verbose_name'] = kwargs.get('verbose_name', None)
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kwargs['rel'] = GenericRel(to,
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related_name=kwargs.pop('related_name', None),
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limit_choices_to=kwargs.pop('limit_choices_to', None),
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symmetrical=kwargs.pop('symmetrical', True))
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# Override content-type/object-id field names on the related class
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self.object_id_field_name = kwargs.pop("object_id_field", "object_id")
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self.content_type_field_name = kwargs.pop("content_type_field", "content_type")
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kwargs['blank'] = True
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kwargs['editable'] = False
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Field.__init__(self, **kwargs)
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def get_manipulator_field_objs(self):
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choices = self.get_choices_default()
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return [curry(forms.SelectMultipleField, size=min(max(len(choices), 5), 15), choices=choices)]
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def get_choices_default(self):
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return Field.get_choices(self, include_blank=False)
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def flatten_data(self, follow, obj = None):
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new_data = {}
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if obj:
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instance_ids = [instance._get_pk_val() for instance in getattr(obj, self.name).all()]
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new_data[self.name] = instance_ids
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return new_data
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def m2m_db_table(self):
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return self.rel.to._meta.db_table
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def m2m_column_name(self):
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return self.object_id_field_name
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def m2m_reverse_name(self):
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return self.model._meta.pk.attname
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def contribute_to_class(self, cls, name):
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super(GenericRelation, self).contribute_to_class(cls, name)
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# Save a reference to which model this class is on for future use
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self.model = cls
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# Add the descriptor for the m2m relation
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setattr(cls, self.name, ReverseGenericRelatedObjectsDescriptor(self))
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def contribute_to_related_class(self, cls, related):
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pass
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def set_attributes_from_rel(self):
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pass
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def get_internal_type(self):
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return "ManyToManyField"
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class ReverseGenericRelatedObjectsDescriptor(object):
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"""
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This class provides the functionality that makes the related-object
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managers available as attributes on a model class, for fields that have
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multiple "remote" values and have a GenericRelation defined in their model
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(rather than having another model pointed *at* them). In the example
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"article.publications", the publications attribute is a
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ReverseGenericRelatedObjectsDescriptor instance.
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"""
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def __init__(self, field):
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self.field = field
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def __get__(self, instance, instance_type=None):
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if instance is None:
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raise AttributeError, "Manager must be accessed via instance"
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# This import is done here to avoid circular import importing this module
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from django.contrib.contenttypes.models import ContentType
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# Dynamically create a class that subclasses the related model's
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# default manager.
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rel_model = self.field.rel.to
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superclass = rel_model._default_manager.__class__
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RelatedManager = create_generic_related_manager(superclass)
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manager = RelatedManager(
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model = rel_model,
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instance = instance,
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symmetrical = (self.field.rel.symmetrical and instance.__class__ == rel_model),
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join_table = backend.quote_name(self.field.m2m_db_table()),
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source_col_name = backend.quote_name(self.field.m2m_column_name()),
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target_col_name = backend.quote_name(self.field.m2m_reverse_name()),
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content_type = ContentType.objects.get_for_model(self.field.model),
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content_type_field_name = self.field.content_type_field_name,
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object_id_field_name = self.field.object_id_field_name
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)
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return manager
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def __set__(self, instance, value):
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if instance is None:
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raise AttributeError, "Manager must be accessed via instance"
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manager = self.__get__(instance)
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manager.clear()
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for obj in value:
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manager.add(obj)
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def create_generic_related_manager(superclass):
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"""
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Factory function for a manager that subclasses 'superclass' (which is a
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Manager) and adds behavior for generic related objects.
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"""
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class GenericRelatedObjectManager(superclass):
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def __init__(self, model=None, core_filters=None, instance=None, symmetrical=None,
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join_table=None, source_col_name=None, target_col_name=None, content_type=None,
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content_type_field_name=None, object_id_field_name=None):
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super(GenericRelatedObjectManager, self).__init__()
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self.core_filters = core_filters or {}
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self.model = model
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self.content_type = content_type
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self.symmetrical = symmetrical
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self.instance = instance
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self.join_table = join_table
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self.join_table = model._meta.db_table
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self.source_col_name = source_col_name
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self.target_col_name = target_col_name
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self.content_type_field_name = content_type_field_name
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self.object_id_field_name = object_id_field_name
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self.pk_val = self.instance._get_pk_val()
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def get_query_set(self):
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query = {
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'%s__pk' % self.content_type_field_name : self.content_type.id,
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'%s__exact' % self.object_id_field_name : self.pk_val,
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}
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return superclass.get_query_set(self).filter(**query)
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def add(self, *objs):
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for obj in objs:
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setattr(obj, self.content_type_field_name, self.content_type)
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setattr(obj, self.object_id_field_name, self.pk_val)
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obj.save()
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add.alters_data = True
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def remove(self, *objs):
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for obj in objs:
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obj.delete()
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remove.alters_data = True
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def clear(self):
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for obj in self.all():
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obj.delete()
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clear.alters_data = True
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def create(self, **kwargs):
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kwargs[self.content_type_field_name] = self.content_type
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kwargs[self.object_id_field_name] = self.pk_val
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obj = self.model(**kwargs)
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obj.save()
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return obj
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create.alters_data = True
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return GenericRelatedObjectManager
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class GenericRel(ManyToManyRel):
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def __init__(self, to, related_name=None, limit_choices_to=None, symmetrical=True):
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self.to = to
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self.num_in_admin = 0
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self.related_name = related_name
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self.filter_interface = None
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self.limit_choices_to = limit_choices_to or {}
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self.edit_inline = False
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self.raw_id_admin = False
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self.symmetrical = symmetrical
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self.multiple = True
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assert not (self.raw_id_admin and self.filter_interface), \
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"Generic relations may not use both raw_id_admin and filter_interface"
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@ -0,0 +1,108 @@
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"""
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33. Generic relations
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Generic relations let an object have a foreign key to any object through a
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content-type/object-id field. A generic foreign key can point to any object,
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be it animal, vegetable, or mineral.
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The cannonical example is tags (although this example implementation is *far*
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from complete).
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"""
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from django.db import models
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from django.contrib.contenttypes.models import ContentType
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class TaggedItem(models.Model):
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"""A tag on an item."""
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tag = models.SlugField()
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content_type = models.ForeignKey(ContentType)
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object_id = models.PositiveIntegerField()
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content_object = models.GenericForeignKey()
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class Meta:
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ordering = ["tag"]
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def __str__(self):
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return self.tag
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class Animal(models.Model):
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common_name = models.CharField(maxlength=150)
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latin_name = models.CharField(maxlength=150)
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tags = models.GenericRelation(TaggedItem)
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def __str__(self):
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return self.common_name
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class Vegetable(models.Model):
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name = models.CharField(maxlength=150)
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is_yucky = models.BooleanField(default=True)
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tags = models.GenericRelation(TaggedItem)
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def __str__(self):
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return self.name
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class Mineral(models.Model):
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name = models.CharField(maxlength=150)
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hardness = models.PositiveSmallIntegerField()
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# note the lack of an explicit GenericRelation here...
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def __str__(self):
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return self.name
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API_TESTS = """
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# Create the world in 7 lines of code...
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>>> lion = Animal(common_name="Lion", latin_name="Panthera leo")
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>>> platypus = Animal(common_name="Platypus", latin_name="Ornithorhynchus anatinus")
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>>> eggplant = Vegetable(name="Eggplant", is_yucky=True)
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>>> bacon = Vegetable(name="Bacon", is_yucky=False)
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>>> quartz = Mineral(name="Quartz", hardness=7)
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>>> for o in (lion, platypus, eggplant, bacon, quartz):
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... o.save()
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# Objects with declared GenericRelations can be tagged directly -- the API
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# mimics the many-to-many API
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>>> lion.tags.create(tag="yellow")
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<TaggedItem: yellow>
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>>> lion.tags.create(tag="hairy")
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<TaggedItem: hairy>
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>>> bacon.tags.create(tag="fatty")
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<TaggedItem: fatty>
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>>> bacon.tags.create(tag="salty")
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<TaggedItem: salty>
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>>> lion.tags.all()
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[<TaggedItem: hairy>, <TaggedItem: yellow>]
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>>> bacon.tags.all()
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[<TaggedItem: fatty>, <TaggedItem: salty>]
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# You can easily access the content object like a foreign key
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>>> t = TaggedItem.objects.get(tag="salty")
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>>> t.content_object
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<Vegetable: Bacon>
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# Recall that the Mineral class doesn't have an explicit GenericRelation
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# defined. That's OK since you can create TaggedItems explicitally.
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>>> tag1 = TaggedItem(content_object=quartz, tag="shiny")
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>>> tag2 = TaggedItem(content_object=quartz, tag="clearish")
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>>> tag1.save()
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>>> tag2.save()
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# However, not having the convience takes a small toll when it comes
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# to do lookups
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>>> from django.contrib.contenttypes.models import ContentType
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>>> ctype = ContentType.objects.get_for_model(quartz)
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>>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id)
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[<TaggedItem: clearish>, <TaggedItem: shiny>]
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# You can set a generic foreign key in the way you'd expect
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>>> tag1.content_object = platypus
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>>> tag1.save()
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>>> platypus.tags.all()
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[<TaggedItem: shiny>]
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>>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id)
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[<TaggedItem: clearish>]
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"""
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