Docs incorrect about related_model for GenericRelation being None

[Amir Keivan Mohtashami]

The documentation says for field.related_model:
If a field has a generic relation (such as a GenericForeignKey or a GenericRelation) then related_model will be None.

However this is not true for GenericRelations. For these fields the related_model points to the model the field relates to just like the reverse of a ForeignKey. The documentation should be fixed, however this means that to the best of my knowledge, there is no way to distinguish between GenericRelation and reverse of a ForeignKey(short of checking if the field is an instance of GenericRelation).

[Tim Graham]

Is the attached patch fine?

[Amir Keivan Mohtashami]

Since GenericRelation is actually a generic field, isn't it better to explicitly exclude it from the rule?

[Tim Graham]

In the patch, I meant to write, "If a field is a GenericForeignKey". (chop extra "generic")

I'm not sure if your comment is suggesting a documentation change or a code change?

[Amir Keivan Mohtashami]

The change you propose will correctly describe the current behavior of Django.

However I don't know whether it is the right approach to change the documentation or would it be better to update the code. Since related_model is set to None for GenericForeignKey it might be reasonable to set it to None for GenericRelation as well.

[Simon Charette]

Since related_model is set to None for GenericForeignKey it might be reasonable to set it to None for GenericRelation as well.

GenericForeignKey.related_model is set to None as it can point to many models by the generic nature of the foreign key. GenericRelation always point to a single reverse model so I believe things should be kept this way.

[Amir Keivan Mohtashami]

I see. Then I guess after removing the additional "generic" the proposed patch should be enough.

[Tim Graham <timograham@…>]

In 55adfc0:

Fixed #27511 -- Corrected Field.related_model docs about GenericRelation.

[Tim Graham <timograham@…>]

In 59ea6fd:

[1.10.x] Fixed #27511 -- Corrected Field.related_model docs about GenericRelation.

Backport of 55adfc076030fc6be2c8d459c4c0a5c91cd4c94c from master