How to make a relation between a local and remote Model

[fxdgear]

In your DRF example you have frontend and backend apps.

In each, you are defining the models for "Articles" "Tags" etc...

But if for example there was a model in the front end, and you wanted to create a relationship to the "backend" between the two, how would you handle this?

[JocelynDelalande]

@fxdgear You can use a custom ForeignKeyField class.

Eg:

class CrossDbForeignKey(models.ForeignKey):
    def validate(self, value, model_instance):
        if self.rel.parent_link:
            return
        super(models.ForeignKey, self).validate(value, model_instance)
        if value is None:
            return

        # Here is the trick, get db relating to fk, not to root model
        using = router.db_for_read(self.rel.to, instance=model_instance)

        qs = self.rel.to._default_manager.using(using).filter(
                **{self.rel.field_name: value}
             )
        qs = qs.complex_filter(self.rel.limit_choices_to)
        if not qs.exists():
            raise exceptions.ValidationError(self.error_messages['invalid'] % {
                'model': self.rel.to._meta.verbose_name, 'pk': value})

It can be used like:

class Membership(models.Model):
    member = CrossDbForeignKey(LdapUser)

I originally wrote this code to reference LDAP models from regular (db) model. More details in this article (in french, sorry).

But you have to be careful, you loose referential integrity.