Django: Why some fields clashes with other

Question

Hi!

I want to create an object that contains 2 links to users. For example

class GameClaim(models.Model):
    target = models.ForeignKey(User)
    claimer = models.ForeignKey(User)
    isAccepted = models.BooleanField()

but I am getting an error when running server:

Accessor for field 'target' clashes with related field 'User.gameclaim_set'. Add a related_name argument to the definition for 'target'. Accessor for field 'claimer' clashes with related field 'User.gameclaim_set'. Add a related_name argument to the definition for 'claimer'.

Please explain why I am getting the error and how to fix it?

Thanks, Oleg

Answer 1

The User model is trying to create two fields with the same name, one for the GameClaims that have that User as the target, and another for the GameClaims that have that User as the claimer. Here's the docs on related_name, which is Django's way of letting you set the names of the attributes so the autogenerated ones don't conflict.

Answer 2

I'm trying not to be rude, but can you not read the error message? It clearly tells you what the problem is and how to fix it.

You have two foreign keys to User. Django automatically creates a reverse relation from User back to GameClaim, which is usually gameclaim_set. However, because you have two FKs, you would have two gameclaim_set attributes, which is obviously impossible. So you need to tell Django what name to use for the generic relation.

Again, how to do this is explained in the error message - use the related_name attribute in the FK definition.

class GameClaim(models.Model):
    target = models.ForeignKey(User, related_name='gameclaim_targets')
    claimer = models.ForeignKey(User, related_name='gameclaim_users')
    isAccepted = models.BooleanField()

Answer 3

If you are using the related_name attribute on a ForeignKey or ManyToManyField, you must always specify a unique reverse name for the field. This would normally cause a problem in abstract base classes, since the fields on this class are included into each of the child classes, with exactly the same values for the attributes (including related_name) each time.

More info: http://docs.djangoproject.com/en/dev/topics/db/models/#be-careful-with-related-name