Django Model set foreign key to a field of another Model

Question

Is there any way to set a foreign key in django to a field of another model?

For example, imagine I have a ValidationRule object. And I want the rule to define what field in another model is to be validated (as well as some other information, such as whether it can be null, a data-type, range, etc.)

Is there a way to store this field-level mapping in django?

Answer 1

Yes and no. The FK relationship is described at the class level, and mirrors the FK association in the database, so you can't add extra information directly in the FK parameter.

Instead, I'd recommend having a string that holds the field name on the other table:

class ValidationRule(models.Model):
    other = models.ForeignKey(OtherModel)
    other_field = models.CharField(max_length=256)

This way, you can obtain the field with:

v = ValidationRule.objects.get(id=1)
field = getattr(v, v.other_field)

Note that if you're using Many-to-Many fields (rather than a One-to-Many), there's built-in support for creating custom intermediary tables to hold meta data with the through option.

Answer 2

I haven't tried this, but it seems that since Django 1.0 you can do something like:

class Foo(models.Model):
    foo = models.ForeignKey(Bar, to_field='bar')

Documentation for this is here.