id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
31357	Stale content types can cause exception in ContentType.get_for_models	Andy Chosak	Biel Frontera	"`ContentType.get_for_models` ([[https://github.com/django/django/blob/e3e48b00127c09eafe6439d980a82fc5c591b673/django/contrib/contenttypes/models.py#L62|source]]) retrieves content types from the database for a given list of models. Due to the way this method works, it's possible to trigger an unexpected `AttributeError` by passing in a list of models whose `(app_label, model_name)` pairs can be permuted to refer to a model with a stale content type in the database.

Consider this example:

1. A project has an app named `foo` with models named `Author` and `Book`. Content types for these exist in the database.
2. A new app named `bar` is created providing an alternate `Book` model. The content type for this also exists.
3. The model `foo.Book` is deleted. The database is migrated, but the stale content type is left behind.

The following code will raise an exception:

{{{
>> from foo.models import Author
>>> from bar.models import Book
>>> from django.contrib.contenttypes.models import ContentType
>>> ContentType.objects.get_for_models(Author, Book)
Traceback (most recent call last):
  File ""<console>"", line 1, in <module>
  File ""/path/to/myproject/lib/python3.6/site-packages/django/contrib/contenttypes/models.py"", line 89, in get_for_models
    opts_models = needed_opts.pop(ct.model_class()._meta, [])
AttributeError: 'NoneType' object has no attribute '_meta'
}}}

This occurs because the `ct.model_class()` call returns `None` for stale content types.

The problem is in [[https://github.com/django/django/blob/e3e48b00127c09eafe6439d980a82fc5c591b673/django/contrib/contenttypes/models.py#L83-L87|this database lookup]] that tries to pull back content types for the models that were passed in. Instead of pulling back only the `ContentType` instances for those models, it filters by `app_label__in=needed_app_labels, model__in=needed_models`. For the above case, this pulls back not just `(foo, Author)` and `(bar, Book)` but also `(foo, Book)`, which in this case is stale.

A fix here could either alter the query to be more specific or check the returned content types to make sure they correspond to one of the desired models."	Bug	closed	contrib.contenttypes	3.0	Normal	fixed			Ready for checkin	1	0	0	0	0	0