django/contrib/contenttypes/generic.py

   1 """
   2 Classes allowing "generic" relations through ContentType and object-id fields.
   3 """
   4
   5 from django.core.exceptions import ObjectDoesNotExist
   6 from django.db import connection
   7 from django.db.models import signals
   8 from django.db import models
   9 from django.db.models.fields.related import RelatedField, Field, ManyToManyRel
  10 from django.db.models.loading import get_model
  11 from django.forms import ModelForm
  12 from django.forms.models import BaseModelFormSet, modelformset_factory, save_instance
  13 from django.contrib.admin.options import InlineModelAdmin, flatten_fieldsets
  14 from django.utils.encoding import smart_unicode
  15
  16 class GenericForeignKey(object):
  17     """
  18     Provides a generic relation to any object through content-type/object-id
  19     fields.
  20     """
  21
  22     def __init__(self, ct_field="content_type", fk_field="object_id"):
  23         self.ct_field = ct_field
  24         self.fk_field = fk_field
  25
  26     def contribute_to_class(self, cls, name):
  27         self.name = name
  28         self.model = cls
  29         self.cache_attr = "_%s_cache" % name
  30         cls._meta.add_virtual_field(self)
  31
  32         # For some reason I don't totally understand, using weakrefs here doesn't work.
  33         signals.pre_init.connect(self.instance_pre_init, sender=cls, weak=False)
  34
  35         # Connect myself as the descriptor for this field
  36         setattr(cls, name, self)
  37
  38     def instance_pre_init(self, signal, sender, args, kwargs, **_kwargs):
  39         """
  40         Handles initializing an object with the generic FK instaed of
  41         content-type/object-id fields.
  42         """
  43         if self.name in kwargs:
  44             value = kwargs.pop(self.name)
  45             kwargs[self.ct_field] = self.get_content_type(obj=value)
  46             kwargs[self.fk_field] = value._get_pk_val()
  47
  48     def get_content_type(self, obj=None, id=None):
  49         # Convenience function using get_model avoids a circular import when
  50         # using this model
  51         ContentType = get_model("contenttypes", "contenttype")
  52         if obj:
  53             return ContentType.objects.get_for_model(obj)
  54         elif id:
  55             return ContentType.objects.get_for_id(id)
  56         else:
  57             # This should never happen. I love comments like this, don't you?
  58             raise Exception("Impossible arguments to GFK.get_content_type!")
  59
  60     def __get__(self, instance, instance_type=None):
  61         if instance is None:
  62             raise AttributeError, u"%s must be accessed via instance" % self.name
  63
  64         try:
  65             return getattr(instance, self.cache_attr)
  66         except AttributeError:
  67             rel_obj = None
  68
  69             # Make sure to use ContentType.objects.get_for_id() to ensure that
  70             # lookups are cached (see ticket #5570). This takes more code than
  71             # the naive ``getattr(instance, self.ct_field)``, but has better
  72             # performance when dealing with GFKs in loops and such.
  73             f = self.model._meta.get_field(self.ct_field)
  74             ct_id = getattr(instance, f.get_attname(), None)
  75             if ct_id:
  76                 ct = self.get_content_type(id=ct_id)
  77                 try:
  78                     rel_obj = ct.get_object_for_this_type(pk=getattr(instance, self.fk_field))
  79                 except ObjectDoesNotExist:
  80                     pass
  81             setattr(instance, self.cache_attr, rel_obj)
  82             return rel_obj
  83
  84     def __set__(self, instance, value):
  85         if instance is None:
  86             raise AttributeError, u"%s must be accessed via instance" % self.related.opts.object_name
  87
  88         ct = None
  89         fk = None
  90         if value is not None:
  91             ct = self.get_content_type(obj=value)
  92             fk = value._get_pk_val()
  93
  94         setattr(instance, self.ct_field, ct)
  95         setattr(instance, self.fk_field, fk)
  96         setattr(instance, self.cache_attr, value)
  97
  98 class GenericRelation(RelatedField, Field):
  99     """Provides an accessor to generic related objects (e.g. comments)"""
 100
 101     def __init__(self, to, **kwargs):
 102         kwargs['verbose_name'] = kwargs.get('verbose_name', None)
 103         kwargs['rel'] = GenericRel(to,
 104                             related_name=kwargs.pop('related_name', None),
 105                             limit_choices_to=kwargs.pop('limit_choices_to', None),
 106                             symmetrical=kwargs.pop('symmetrical', True))
 107
 108         # By its very nature, a GenericRelation doesn't create a table.
 109         self.creates_table = False
 110
 111         # Override content-type/object-id field names on the related class
 112         self.object_id_field_name = kwargs.pop("object_id_field", "object_id")
 113         self.content_type_field_name = kwargs.pop("content_type_field", "content_type")
 114
 115         kwargs['blank'] = True
 116         kwargs['editable'] = False
 117         kwargs['serialize'] = False
 118         Field.__init__(self, **kwargs)
 119
 120     def get_choices_default(self):
 121         return Field.get_choices(self, include_blank=False)
 122
 123     def value_to_string(self, obj):
 124         qs = getattr(obj, self.name).all()
 125         return smart_unicode([instance._get_pk_val() for instance in qs])
 126
 127     def m2m_db_table(self):
 128         return self.rel.to._meta.db_table
 129
 130     def m2m_column_name(self):
 131         return self.object_id_field_name
 132
 133     def m2m_reverse_name(self):
 134         return self.model._meta.pk.column
 135
 136     def contribute_to_class(self, cls, name):
 137         super(GenericRelation, self).contribute_to_class(cls, name)
 138
 139         # Save a reference to which model this class is on for future use
 140         self.model = cls
 141
 142         # Add the descriptor for the m2m relation
 143         setattr(cls, self.name, ReverseGenericRelatedObjectsDescriptor(self))
 144
 145     def contribute_to_related_class(self, cls, related):
 146         pass
 147
 148     def set_attributes_from_rel(self):
 149         pass
 150
 151     def get_internal_type(self):
 152         return "ManyToManyField"
 153
 154     def db_type(self):
 155         # Since we're simulating a ManyToManyField, in effect, best return the
 156         # same db_type as well.
 157         return None
 158
 159     def extra_filters(self, pieces, pos, negate):
 160         """
 161         Return an extra filter to the queryset so that the results are filtered
 162         on the appropriate content type.
 163         """
 164         if negate:
 165             return []
 166         ContentType = get_model("contenttypes", "contenttype")
 167         content_type = ContentType.objects.get_for_model(self.model)
 168         prefix = "__".join(pieces[:pos + 1])
 169         return [("%s__%s" % (prefix, self.content_type_field_name),
 170             content_type)]
 171
 172 class ReverseGenericRelatedObjectsDescriptor(object):
 173     """
 174     This class provides the functionality that makes the related-object
 175     managers available as attributes on a model class, for fields that have
 176     multiple "remote" values and have a GenericRelation defined in their model
 177     (rather than having another model pointed *at* them). In the example
 178     "article.publications", the publications attribute is a
 179     ReverseGenericRelatedObjectsDescriptor instance.
 180     """
 181     def __init__(self, field):
 182         self.field = field
 183
 184     def __get__(self, instance, instance_type=None):
 185         if instance is None:
 186             raise AttributeError, "Manager must be accessed via instance"
 187
 188         # This import is done here to avoid circular import importing this module
 189         from django.contrib.contenttypes.models import ContentType
 190
 191         # Dynamically create a class that subclasses the related model's
 192         # default manager.
 193         rel_model = self.field.rel.to
 194         superclass = rel_model._default_manager.__class__
 195         RelatedManager = create_generic_related_manager(superclass)
 196
 197         qn = connection.ops.quote_name
 198
 199         manager = RelatedManager(
 200             model = rel_model,
 201             instance = instance,
 202             symmetrical = (self.field.rel.symmetrical and instance.__class__ == rel_model),
 203             join_table = qn(self.field.m2m_db_table()),
 204             source_col_name = qn(self.field.m2m_column_name()),
 205             target_col_name = qn(self.field.m2m_reverse_name()),
 206             content_type = ContentType.objects.get_for_model(self.field.model),
 207             content_type_field_name = self.field.content_type_field_name,
 208             object_id_field_name = self.field.object_id_field_name
 209         )
 210
 211         return manager
 212
 213     def __set__(self, instance, value):
 214         if instance is None:
 215             raise AttributeError, "Manager must be accessed via instance"
 216
 217         manager = self.__get__(instance)
 218         manager.clear()
 219         for obj in value:
 220             manager.add(obj)
 221
 222 def create_generic_related_manager(superclass):
 223     """
 224     Factory function for a manager that subclasses 'superclass' (which is a
 225     Manager) and adds behavior for generic related objects.
 226     """
 227
 228     class GenericRelatedObjectManager(superclass):
 229         def __init__(self, model=None, core_filters=None, instance=None, symmetrical=None,
 230                      join_table=None, source_col_name=None, target_col_name=None, content_type=None,
 231                      content_type_field_name=None, object_id_field_name=None):
 232
 233             super(GenericRelatedObjectManager, self).__init__()
 234             self.core_filters = core_filters or {}
 235             self.model = model
 236             self.content_type = content_type
 237             self.symmetrical = symmetrical
 238             self.instance = instance
 239             self.join_table = join_table
 240             self.join_table = model._meta.db_table
 241             self.source_col_name = source_col_name
 242             self.target_col_name = target_col_name
 243             self.content_type_field_name = content_type_field_name
 244             self.object_id_field_name = object_id_field_name
 245             self.pk_val = self.instance._get_pk_val()
 246
 247         def get_query_set(self):
 248             query = {
 249                 '%s__pk' % self.content_type_field_name : self.content_type.id,
 250                 '%s__exact' % self.object_id_field_name : self.pk_val,
 251             }
 252             return superclass.get_query_set(self).filter(**query)
 253
 254         def add(self, *objs):
 255             for obj in objs:
 256                 setattr(obj, self.content_type_field_name, self.content_type)
 257                 setattr(obj, self.object_id_field_name, self.pk_val)
 258                 obj.save()
 259         add.alters_data = True
 260
 261         def remove(self, *objs):
 262             for obj in objs:
 263                 obj.delete()
 264         remove.alters_data = True
 265
 266         def clear(self):
 267             for obj in self.all():
 268                 obj.delete()
 269         clear.alters_data = True
 270
 271         def create(self, **kwargs):
 272             kwargs[self.content_type_field_name] = self.content_type
 273             kwargs[self.object_id_field_name] = self.pk_val
 274             return super(GenericRelatedObjectManager, self).create(**kwargs)
 275         create.alters_data = True
 276
 277     return GenericRelatedObjectManager
 278
 279 class GenericRel(ManyToManyRel):
 280     def __init__(self, to, related_name=None, limit_choices_to=None, symmetrical=True):
 281         self.to = to
 282         self.related_name = related_name
 283         self.limit_choices_to = limit_choices_to or {}
 284         self.symmetrical = symmetrical
 285         self.multiple = True
 286
 287 class BaseGenericInlineFormSet(BaseModelFormSet):
 288     """
 289     A formset for generic inline objects to a parent.
 290     """
 291     ct_field_name = "content_type"
 292     ct_fk_field_name = "object_id"
 293
 294     def __init__(self, data=None, files=None, instance=None, save_as_new=None):
 295         opts = self.model._meta
 296         self.instance = instance
 297         self.rel_name = '-'.join((
 298             opts.app_label, opts.object_name.lower(),
 299             self.ct_field.name, self.ct_fk_field.name,
 300         ))
 301         super(BaseGenericInlineFormSet, self).__init__(
 302             queryset=self.get_queryset(), data=data, files=files,
 303             prefix=self.rel_name
 304         )
 305
 306     def get_queryset(self):
 307         # Avoid a circular import.
 308         from django.contrib.contenttypes.models import ContentType
 309         if self.instance is None:
 310             return self.model._default_manager.empty()
 311         return self.model._default_manager.filter(**{
 312             self.ct_field.name: ContentType.objects.get_for_model(self.instance),
 313             self.ct_fk_field.name: self.instance.pk,
 314         })
 315
 316     def save_new(self, form, commit=True):
 317         # Avoid a circular import.
 318         from django.contrib.contenttypes.models import ContentType
 319         kwargs = {
 320             self.ct_field.get_attname(): ContentType.objects.get_for_model(self.instance).pk,
 321             self.ct_fk_field.get_attname(): self.instance.pk,
 322         }
 323         new_obj = self.model(**kwargs)
 324         return save_instance(form, new_obj, commit=commit)
 325
 326 def generic_inlineformset_factory(model, form=ModelForm,
 327                                   formset=BaseGenericInlineFormSet,
 328                                   ct_field="content_type", fk_field="object_id",
 329                                   fields=None, exclude=None,
 330                                   extra=3, can_order=False, can_delete=True,
 331                                   max_num=0,
 332                                   formfield_callback=lambda f: f.formfield()):
 333     """
 334     Returns an ``GenericInlineFormSet`` for the given kwargs.
 335
 336     You must provide ``ct_field`` and ``object_id`` if they different from the
 337     defaults ``content_type`` and ``object_id`` respectively.
 338     """
 339     opts = model._meta
 340     # Avoid a circular import.
 341     from django.contrib.contenttypes.models import ContentType
 342     # if there is no field called `ct_field` let the exception propagate
 343     ct_field = opts.get_field(ct_field)
 344     if not isinstance(ct_field, models.ForeignKey) or ct_field.rel.to != ContentType:
 345         raise Exception("fk_name '%s' is not a ForeignKey to ContentType" % ct_field)
 346     fk_field = opts.get_field(fk_field) # let the exception propagate
 347     if exclude is not None:
 348         exclude.extend([ct_field.name, fk_field.name])
 349     else:
 350         exclude = [ct_field.name, fk_field.name]
 351     FormSet = modelformset_factory(model, form=form,
 352                                    formfield_callback=formfield_callback,
 353                                    formset=formset,
 354                                    extra=extra, can_delete=can_delete, can_order=can_order,
 355                                    fields=fields, exclude=exclude, max_num=max_num)
 356     FormSet.ct_field = ct_field
 357     FormSet.ct_fk_field = fk_field
 358     return FormSet
 359
 360 class GenericInlineModelAdmin(InlineModelAdmin):
 361     ct_field = "content_type"
 362     ct_fk_field = "object_id"
 363     formset = BaseGenericInlineFormSet
 364
 365     def get_formset(self, request, obj=None):
 366         if self.declared_fieldsets:
 367             fields = flatten_fieldsets(self.declared_fieldsets)
 368         else:
 369             fields = None
 370         defaults = {
 371             "ct_field": self.ct_field,
 372             "fk_field": self.ct_fk_field,
 373             "form": self.form,
 374             "formfield_callback": self.formfield_for_dbfield,
 375             "formset": self.formset,
 376             "extra": self.extra,
 377             "can_delete": True,
 378             "can_order": False,
 379             "fields": fields,
 380         }
 381         return generic_inlineformset_factory(self.model, **defaults)
 382
 383 class GenericStackedInline(GenericInlineModelAdmin):
 384     template = 'admin/edit_inline/stacked.html'
 385
 386 class GenericTabularInline(GenericInlineModelAdmin):
 387     template = 'admin/edit_inline/tabular.html'