The `model` attribute of image fields doesn't point to concrete model.

[Matthias Kestenholz]

In Django 3.1 and before, one could use the model attribute of image fields to find the concrete model the image field belongs to.

This isn't possible in 3.2 anymore, and I bisected the change to the fix of #31701.

I found this while investigating a CI failure of django-imagefield ​https://travis-ci.org/github/matthiask/django-imagefield/jobs/710794644

I'm not sure whether this is a bug or whether it is an intentional change. If it is the later, is there an alternative to find the concrete model an image field belongs to? I'm classifying this as a bug because the change made model and field introspection harder than it was before. Also, since behavior changed #31701 may possibly not be classified as a cleanup/optimization anymore...

[Mariusz Felisiak]

Thanks for the report! I think we should restore contribute_to_class() but with attname:

diff --git a/django/db/models/fields/files.py b/django/db/models/fields/files.py
index b064202ee3..e10a5bb6d9 100644
--- a/django/db/models/fields/files.py
+++ b/django/db/models/fields/files.py
@@ -299,6 +299,10 @@ class FileField(Field):
             file.save(file.name, file.file, save=False)
         return file
 
+    def contribute_to_class(self, cls, name, **kwargs):
+        super().contribute_to_class(cls, name, **kwargs)
+        setattr(cls, self.attname, self.descriptor_class(self))
+
     def generate_filename(self, instance, filename):
         """
         Apply (if callable) or prepend (if a string) upload_to to the filename,

Regression in a93425a37f4defdb31d4ca96bb3bf6da21f0b5ce.

Reproduced at f65454801bfa13fc043fee0aca8f49af41380683.

[Matthias Kestenholz]

Yes, the proposed fix works for me.

[Mariusz Felisiak]

Great, would you like to prepare a patch (with regression tests)?

[Matthias Kestenholz]

Sure! Here's a pull request:

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In c1f8d87b:

Fixed #31812 -- Fixed FileField.model for fields defined in abstract models.

Regression in a93425a37f4defdb31d4ca96bb3bf6da21f0b5ce.