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
35654	SystemCheckError on GenericRelation with lazy reference	Giannis Terzopoulos		"Let's consider having 2 apps, `core` and `bookmarks`. Then I add a new `TaggetItem` model to `core`:
{{{#!python
class TaggedItem(models.Model):
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey()
}}}

and a new `Bookmark` model to `bookmarks`:
{{{#!python
class Bookmark(models.Model):
    tags = GenericRelation('core.TagedItem')
}}}

Running `makemigrations` here I am getting:
{{{
SystemCheckError: System check identified some issues:

ERRORS:
<function GenericRelation.contribute_to_class.<locals>.make_generic_foreign_order_accessors at 0x7a08cdb98e00>: (models.E022) <function GenericRelation.contribute_to_class.<locals>.make_generic_foreign_order_accessors at 0x7a08cdb98e00> contains a lazy reference to core.tageditem, but app 'core' doesn't provide model 'tageditem'.
bookmarks.Bookmark.tags: (fields.E307) The field bookmarks.Bookmark.tags was declared with a lazy reference to 'core.tageditem', but app 'core' doesn't provide model 'tageditem'.
}}}

The same happens if I `makemigrations` after adding TaggedItem, then add Bookmark and run `makemigrations` again.
It doesn't happen if I `migrate` for TaggedItem, then add Bookmark and `makemigrations`.

It also doesn't happen if I import `TaggedItem` and use that in `GenericRelation`:
{{{#!python
from core.models import TaggedItem


class Bookmark(models.Model):
    tags = GenericRelation(TaggedItem)
}}}

The downside of this in my initial use case was that I would have to work around circular import errors, which wasn't easily doable. 

Finally, having both models in the same app/models.py doesn't trigger the error either, so it seems to be as if something is missing here."	Bug	new	Database layer (models, ORM)	5.0	Normal				Unreviewed	0	0	0	0	0	0