ValueError: Related model u'app.model' cannot be resolved

Question

I have two applications (ook and eek say) and I want to use a foreign key to a model in ook from a model in eek. Both are in INSTALLED_APPS with ook first.

In ook.models.py, i have:

class Fubar(models.Model):     ... 

In eek.models.py, I have:

class monkey(models.Model):     external = models.ForeignKey('ook.Fubar', blank=True, null=True)     ... 

The migration generated is:

class Migration(migrations.Migration):      dependencies = [         ('eek', '0002_auto_20151029_1040'),     ]      operations = [         migrations.AlterField(             model_name='monkey',             name='external',             field=models.ForeignKey(blank=True, to='ook.Fubar', null=True),         ),     ] 

When I run the migration, I get this error:

   ...    1595             raise ValueError('Foreign Object from and to fields must be the same non-zero length')    1596         if isinstance(self.rel.to, six.string_types): -> 1597             raise ValueError('Related model %r cannot be resolved' % self.rel.to)    1598         related_fields = []    1599         for index in range(len(self.from_fields)): ValueError: Related model u'ook.Fubar' cannot be resolved 

What am I doing wrong?

Answer 1

Because You have ForeignKey in operations, You must add a ook to dependencies:

dependencies = [     ('ook', '__first__'),     ('eek', '0002_auto_20151029_1040'), ] 

Django migrations have two "magic" values:

• __first__ - get module first migration
• __latest__ - get module latest migration