proposal: add special subclass of ForeignKey for storing ContentTypes

[Sergey Fedoseev]

Hi all,

Some time ago I created 'new feature` ticket and Tim Graham asked me to write here to get some feedback on the idea. So here it is.

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

For example, we have a model:

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

In comparison with ForeignKey ContentTypeField will have these features:

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

2. ContentTypeField will support lookups on the model classes (on model instances too?):

ModelWithContentType.objects.filter(ct=FooModel) vs.

ModelWithContentType.objects.filter(ct=ContentType.objects.get_for_model(FooModel))

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

3. Creation using a model class as a value (not sure if it's useful actually):

ModelWithContentType.objects.create(ct=FooModel)




Here's ​rough implementation.

[Asif Saifuddin]

Hi Sergey,

I was also wondering why GenericForeignKey don't have direct subclass of ForeignKey while writing a dep about field API improvement. Though I am not 100% sure your implementation.

Thanks for bringing it up.

[Adam Johnson]

Sergey, I like the idea. It at least serves as a demonstration of what can be done with custom fields. The PoC shows it's not too much code either. Would you be looking to replace the existing FK's to ContentType too, e.g. in Admin and Auth?

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