Wrong resolution of content type id for proxy models in ModelAdmin

[alejandro]

I have a number of proxy models that I want to present separately in the admin interface. A simplified example would be:

class Accommodation(models.Model):
    name = models.CharField(max_length=10)

class Inn(Accommodation):
    class Meta:
        proxy = True

class Hotel(Accommodation):
    class Meta:
        proxy = True


admin.site.register(Inn)
admin.site.register(Hotel)

However, due to how ModelAdmin gets the content type of the models the retrieved content type instances will always be those corresponding to Accommodation. This causes several problems:

• The log entries shown in the admin index will have broken links because log entries have the content type id of Accommodation instead of Inn or Hotel.
• In the change form, the content_type_id context variable will be the one of Accommodation content type, causing the "View on site" link not to work.

I'm not sure wether there are more cases where getting the content type from the concrete model breaks things in the admin. A naive fix would be to pass for_concrete_model=False for every ContentType.objects.get_for_model call in ModelAdmin code but I'm not aware of the consequences of that since I'm not familiar enough with Django internals.

[Tim Graham]

Here is a ​PR for a duplicate ticket (#21260). Like the OP, I haven't look into whether or not this is the best fix and it also lacks tests.

[buremba]

I added test for this bug. ​https://github.com/django/django/pull/1728

[Baptiste Mispelon]

As noted in the comments on github, the proposed pull request needs improvement.

[alejandro]

I've written an updated patch and submitted a PR: ​https://github.com/django/django/pull/2518

[Tim Graham <timograham@…>]

In 7a7f6fccae7470efc515ecd7efb917f5cf3f8b87:

Fixed #21084 -- Used proxy model's content type for admin log entries.

[Tim Graham <timograham@…>]

In 5e74d6cf0a4fa0caa51e77af77d55c2572f0917d:

[1.7.x] Fixed #21084 -- Used proxy model's content type for admin log entries.

Backport of 7a7f6fccae from master

[Tim Graham <timograham@…>]

In 3cba90f22a9120ebf9b00d1d074b8fb2152ecd2e:

Fixed #21084 -- Used proxy model's content type for admin log entries.

(the previous commit included only the test)

[Tim Graham <timograham@…>]

In 32c857908998503cd595311eebc9256d44f65803:

[1.7.x] Fixed #21084 -- Used proxy model's content type for admin log entries.

(the previous commit included only the test)

Backport of 3cba90f22a from master