Question

I have the following two models:

class Provider(models.Model):
    provider = models.CharField(max_length=100, unique=True)

class UserProfile(models.Model):
    user = models.ForeignKey(User, unique=True)
    provider = models.ForeignKey(Provider, db_column='provider')

When I try and save a new object, I get a FK error:

>>> from main_app.models import User, UserProfile, Provider
>>> p=Provider.objects.get(id=2)
>>> u=User.objects.get(id=1)
>>> p
<Provider: ACME>
>>> u
<User: [e-mail]>
>>> UserProfile.objects.create(user=u, provider=p)
    raise errorclass, errorvalue
IntegrityError: (1452, 'Cannot add or update a child row: a foreign key constraint fails
(`premiere`.`main_app_userprofile`, CONSTRAINT `provider_refs_provider_f2a06b37` 
FOREIGN KEY (`provider`) REFERENCES `main_app_provider` (`provider`))')

What am I doing incorrectly here?

Answer 1

It seems MySQL expects your foreign key provider to reference the column provider of the main_app_provider table. However, Django will store a reference to the primary key (id if not specified otherwise) in the foreign key. Try setting

provider = models.CharField(max_length=100, primary_key=True)

and rebuild your database, or change the MySQL foreign key constraint to use id instead of provider.