from django.db import models # No related name is needed here, since symmetrical relations are not # explicitly reversible. class SelfRefer(models.Model): name = models.CharField(max_length=10) references = models.ManyToManyField('self') related = models.ManyToManyField('self') def __unicode__(self): return self.name class Tag(models.Model): name = models.CharField(max_length=10) def __unicode__(self): return self.name # A related_name is required on one of the ManyToManyField entries here because # they are both addressable as reverse relations from Tag. class Entry(models.Model): name = models.CharField(max_length=10) topics = models.ManyToManyField(Tag) related = models.ManyToManyField(Tag, related_name="similar") def __unicode__(self): return self.name __test__ = {"regressions": """ # Multiple m2m references to the same model or a different model must be # distinguished when accessing the relations through an instance attribute. >>> s1 = SelfRefer.objects.create(name='s1') >>> s2 = SelfRefer.objects.create(name='s2') >>> s3 = SelfRefer.objects.create(name='s3') >>> s1.references.add(s2) >>> s1.related.add(s3) >>> e1 = Entry.objects.create(name='e1') >>> t1 = Tag.objects.create(name='t1') >>> t2 = Tag.objects.create(name='t2') >>> e1.topics.add(t1) >>> e1.related.add(t2) >>> s1.references.all() [] >>> s1.related.all() [] >>> e1.topics.all() [] >>> e1.related.all() [] # The secret internal related names for self-referential many-to-many fields # shouldn't appear in the list when an error is made. >>> SelfRefer.objects.filter(porcupine='fred') Traceback (most recent call last): ... FieldError: Cannot resolve keyword 'porcupine' into field. Choices are: id, name, references, related """ }