add special field for storing content types

[Sergey Fedoseev]

ContentType model is quite specific, so we could add the subclass of ForeignKey field with some specific features.

For example we have such model:

class ModelWithContentTypeField(models.Model):
    ct = ContentTypeField(on_delete=models.CASCADE)

In comparison with ForeignKey ContentTypeField will have these features:

1. ModelWithContentTypeField.objects.first().ct will use content types cache.

2. ContentTypeField will support lookups on the model classes:

ModelWithContentTypeField.objects.filter(ct=FooModel) vs ModelWithContentTypeField.objects.filter(ct=ContentType.objects.get_for_model(FooModel))

ModelWithContentTypeField.objects.filter(ct__in=[FooModel, BarModel]) vs
ModelWithContentTypeField.objects.filter(ct__in=[ContentType.objects.get_for_model(model) in [FooModel, BarModel]])

3. Creation using a model class as a value:

ModelWithContentTypeField.objects.create(ct=FooModel)

Here's ​rough implementation.

[Jani Tiainen]

Does this feature require changes in Django core which prevents implementing this as an external app? I only saw quite small change in actual Django core.

[Tim Graham]

Sergey, could you write to the DevelopersMailingList to get feedback on the idea?

[Marten Kenbeek]

Note that you shouldn't hardcode the ContentType class anywhere, or migrations will refer to the wrong model. Use self.related_model in the field, and self.field.related_model in the descriptor.

[Sergey Fedoseev]

Replying to Marten Kenbeek:

Note that you shouldn't hardcode the ContentType class anywhere, or migrations will refer to the wrong model. Use self.related_model in the field, and self.field.related_model in the descriptor.

Thanks for the hint!