""" 34. Generic relations Generic relations let an object have a foreign key to any object through a content-type/object-id field. A ``GenericForeignKey`` field can point to any object, be it animal, vegetable, or mineral. The canonical example is tags (although this example implementation is *far* from complete). """ from django.db import models from django.contrib.contenttypes.models import ContentType from django.contrib.contenttypes import generic class TaggedItem(models.Model): """A tag on an item.""" tag = models.SlugField() content_type = models.ForeignKey(ContentType) object_id = models.PositiveIntegerField() content_object = generic.GenericForeignKey() class Meta: ordering = ["tag"] def __unicode__(self): return self.tag class Comparison(models.Model): """ A model that tests having multiple GenericForeignKeys """ comparative = models.CharField(max_length=50) content_type1 = models.ForeignKey(ContentType, related_name="comparative1_set") object_id1 = models.PositiveIntegerField() content_type2 = models.ForeignKey(ContentType, related_name="comparative2_set") object_id2 = models.PositiveIntegerField() first_obj = generic.GenericForeignKey(ct_field="content_type1", fk_field="object_id1") other_obj = generic.GenericForeignKey(ct_field="content_type2", fk_field="object_id2") def __unicode__(self): return u"%s is %s than %s" % (self.first_obj, self.comparative, self.other_obj) class Animal(models.Model): common_name = models.CharField(max_length=150) latin_name = models.CharField(max_length=150) tags = generic.GenericRelation(TaggedItem) comparisons = generic.GenericRelation(Comparison, object_id_field="object_id1", content_type_field="content_type1") def __unicode__(self): return self.common_name class Vegetable(models.Model): name = models.CharField(max_length=150) is_yucky = models.BooleanField(default=True) tags = generic.GenericRelation(TaggedItem) def __unicode__(self): return self.name class Mineral(models.Model): name = models.CharField(max_length=150) hardness = models.PositiveSmallIntegerField() # note the lack of an explicit GenericRelation here... def __unicode__(self): return self.name __test__ = {'API_TESTS':""" # Create the world in 7 lines of code... >>> lion = Animal(common_name="Lion", latin_name="Panthera leo") >>> platypus = Animal(common_name="Platypus", latin_name="Ornithorhynchus anatinus") >>> eggplant = Vegetable(name="Eggplant", is_yucky=True) >>> bacon = Vegetable(name="Bacon", is_yucky=False) >>> quartz = Mineral(name="Quartz", hardness=7) >>> for o in (lion, platypus, eggplant, bacon, quartz): ... o.save() # Objects with declared GenericRelations can be tagged directly -- the API # mimics the many-to-many API. >>> bacon.tags.create(tag="fatty") >>> bacon.tags.create(tag="salty") >>> lion.tags.create(tag="yellow") >>> lion.tags.create(tag="hairy") >>> lion.tags.all() [, ] >>> bacon.tags.all() [, ] # You can easily access the content object like a foreign key. >>> t = TaggedItem.objects.get(tag="salty") >>> t.content_object # Recall that the Mineral class doesn't have an explicit GenericRelation # defined. That's OK, because you can create TaggedItems explicitly. >>> tag1 = TaggedItem(content_object=quartz, tag="shiny") >>> tag2 = TaggedItem(content_object=quartz, tag="clearish") >>> tag1.save() >>> tag2.save() # However, excluding GenericRelations means your lookups have to be a bit more # explicit. >>> from django.contrib.contenttypes.models import ContentType >>> ctype = ContentType.objects.get_for_model(quartz) >>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id) [, ] # You can set a generic foreign key in the way you'd expect. >>> tag1.content_object = platypus >>> tag1.save() >>> platypus.tags.all() [] >>> TaggedItem.objects.filter(content_type__pk=ctype.id, object_id=quartz.id) [] # If you delete an object with an explicit Generic relation, the related # objects are deleted when the source object is deleted. # Original list of tags: >>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()] [(u'clearish', , 1), (u'fatty', , 2), (u'hairy', , 1), (u'salty', , 2), (u'shiny', , 2), (u'yellow', , 1)] >>> lion.delete() >>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()] [(u'clearish', , 1), (u'fatty', , 2), (u'salty', , 2), (u'shiny', , 2)] # If Generic Relation is not explicitly defined, any related objects # remain after deletion of the source object. >>> quartz.delete() >>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()] [(u'clearish', , 1), (u'fatty', , 2), (u'salty', , 2), (u'shiny', , 2)] # If you delete a tag, the objects using the tag are unaffected # (other than losing a tag) >>> tag = TaggedItem.objects.get(id=1) >>> tag.delete() >>> bacon.tags.all() [] >>> [(t.tag, t.content_type, t.object_id) for t in TaggedItem.objects.all()] [(u'clearish', , 1), (u'salty', , 2), (u'shiny', , 2)] >>> ctype = ContentType.objects.get_for_model(lion) >>> Animal.objects.filter(tags__content_type=ctype) [] # Simple tests for multiple GenericForeignKeys # only uses one model, since the above tests should be sufficient. >>> tiger, cheetah, bear = Animal(common_name="tiger"), Animal(common_name="cheetah"), Animal(common_name="bear") >>> for o in [tiger, cheetah, bear]: o.save() # Create directly >>> Comparison(first_obj=cheetah, other_obj=tiger, comparative="faster").save() >>> Comparison(first_obj=tiger, other_obj=cheetah, comparative="cooler").save() # Create using GenericRelation >>> tiger.comparisons.create(other_obj=bear, comparative="cooler") >>> tiger.comparisons.create(other_obj=cheetah, comparative="stronger") >>> cheetah.comparisons.all() [] # Filtering works >>> tiger.comparisons.filter(comparative="cooler") [, ] # Filtering and deleting works >>> subjective = ["cooler"] >>> tiger.comparisons.filter(comparative__in=subjective).delete() >>> Comparison.objects.all() [, ] # If we delete cheetah, Comparisons with cheetah as 'first_obj' will be deleted # since Animal has an explicit GenericRelation to Comparison through first_obj. # Comparisons with cheetah as 'other_obj' will not be deleted. >>> cheetah.delete() >>> Comparison.objects.all() [] # GenericInlineFormSet tests ################################################## >>> from django.contrib.contenttypes.generic import generic_inlineformset_factory >>> GenericFormSet = generic_inlineformset_factory(TaggedItem, extra=1) >>> formset = GenericFormSet(instance=Animal()) >>> for form in formset.forms: ... print form.as_p()

>>> formset = GenericFormSet(instance=platypus) >>> for form in formset.forms: ... print form.as_p()

"""}