#35654: SystemCheckError on GenericRelation with lazy reference
-------------------------------------+-------------------------------------
Reporter: Giannis Terzopoulos | Owner: (none)
Type: Bug | Status: new
Component: Database layer | Version: 5.0
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Description changed by Giannis Terzopoulos:
Old description:
> 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.
New description:
Let's consider having 2 apps, `core` and `bookmarks`. Then I add a new
`TaggedItem` 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 and using the ''lazy
reference'' GenericRelation doesn't trigger the error either. So it seems
to me as if something is missing here.
--
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Ticket URL: <https://code.djangoproject.com/ticket/35654#comment:1>
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