Related models cannot have split() method

[Mitar]

Related models cannot have split() method because add_lazy_relation (in db/models/fields/related.py) assumes that something with split() method must be string. I would propose that:

        try:
            app_label, model_name = relation.split(".")
        except ValueError:

is changed to:

        try:
            if isinstance(relation, ModelBase):
                raise ValueError
            app_label, model_name = relation.split(".")
        except ValueError:

[Carl Meyer]

Not sure the proposed patch is the best option, but this should certainly be fixed.

[Jonas Obrist]

I tried to reproduce the problem, but couldn't do so, what is needed to have this problem happen?

[Mitar]

You have to check when add_lazy_relation is called with class as first argument. I find two such cases:

• in RelatedField's contribute_to_class if other._meta.pk is None
• if order_with_respect_to is configured

I do not remember how I triggered the first case. But the second case happens with, for example:

class RelatedModel(models.Model):
    foobar = models.IntegerField()

    def split(self):
        pass

class SomeModel(models.Model):
    related_field = models.ForeignKey(RelatedModel)

    class Meta:
        order_with_respect_to = 'related_field'

[Jonas Obrist]

tests & fix

[Aymeric Augustin]

Apparently, the test passes without the fix in django/db/models/fields/related.py.

[Tim Graham]

It looks to me like the current code shouldn't have this problem.

​https://github.com/django/django/blob/293fd5da5b8c7b79bd34ef793ab45c1bb8ac69ea/django/db/models/fields/related.py#L62-L65