How to work around lack of support for foreign keys across databases in Django

Question

I know Django does not support foreign keys across multiple databases (originally Django 1.3 docs)

But I\'m looking for a workaround.

What doesn\'t work

Answer 1

I have a new solution for django v1.10. There are two parts. It works with django.admin and django.rest-framework.

1. Inherit the ForeignKey class and create ForeignKeyAcrossDb, and override the validate() function, based on this ticket and this post.

class ForeignKeyAcrossDb(models.ForeignKey):
        def validate(self, value, model_instance):
            if self.remote_field.parent_link:
                return
            super(models.ForeignKey, self).validate(value, model_instance)
            if value is None:
                return
            using = router.db_for_read(self.remote_field.model, instance=model_instance)
            qs = self.remote_field.model._default_manager.using(using).filter(
                **{self.remote_field.field_name: value}
            )
            qs = qs.complex_filter(self.get_limit_choices_to())
            if not qs.exists():
                raise exceptions.ValidationError(
                    self.error_messages['invalid'],
                    code='invalid',
                    params={
                        'model': self.remote_field.model._meta.verbose_name, 'pk': value,
                        'field': self.remote_field.field_name, 'value': value,
                    },  # 'pk' is included for backwards compatibility
                )

2. In field declaration, use db_constraint=False, for example,

album=ForeignKeyAcrossDb(Singer, db_constraint=False, on_delete=models.DO_NOTHING)