How can I have two foreign keys to the same model in Django?

51
votes

I want to have two foreign keys to the same model:

class Test(models.model):
    example1 = models.ForeignKey(Example)
    example2 = models.ForeignKey(Example)

I get errors like:

Accessor for field 'example1' clashes with related field 'Example.test_set'. Add a related_name argument to the definition for 'example1'.

4
djangodjango-models

4 Answers

28
votes

Django uses some python magic to define relationships between models, some of which involves using the name of the models in the relationships (that's where the 'test' in 'test__set' is coming from.) What's happening, I would guess, is that it's trying to put "test__set" in the Example model twice, once for each foreign key you've got defined.

The error message suggests something to try: define a related_name argument (overriding one of those 'test_set's) that it can use instead of auto-generating two clashing names.

More info here: page has been removed

Current page relating to model relationships: https://docs.djangoproject.com/en/2.0/ref/models/fields/#module-django.db.models.fields.related

121
votes

Try using related_name:

class Test(models.model):
    example1 = models.ForeignKey('Example', related_name='example1')
    example2 = models.ForeignKey('Example', related_name='example2')
8
votes

Just do what the error message tells you to do, and if you're unsure what that means, consult the documentation for related_name.

4
votes

In django 2.0 Try this:

user = models.ForeignKey(User, on_delete=models.PROTECT, null=True,  related_name='user')
paper = models.ForeignKey(paperRecord, on_delete=models.PROTECT, null=True,  related_name='paper')