#36183: Model o2o inheritance with abstract models does not "evaluate" a lazy
relationship
-------------------------------------+-------------------------------------
Reporter: BeryCZ | Owner: (none)
Type: Bug | Status: closed
Component: Database layer | Version: 5.1
(models, ORM) |
Severity: Normal | Resolution: invalid
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Natalia Bidart):
* resolution: => invalid
* status: new => closed
Comment:
Hello BeryCZ, thank you for this report. I've analyzed your models and I
fear that the issue is the complex inheritance that you have proposed.
Specifically, you cannot have a model (`ArticlePage`) that both inherits
from `Page` and has a `OneToOneField` to `Page`. Without understanding
your use case, it feels like a possible solution would be for your "pages"
to have a FK to "page types" (instead of the other way around with the 1-1
field).
Your model definitions create an inheritance conflict:
1. `AbstractPageType` expects a separate `Page` instance (this means every
model that inherits from `AbstractPageType` must have a separate `Page`
instance linked via the `page` field).
2. `ArticlePage` is also inheriting `Page`, which means Django expects
`ArticlePage` itself to be a `Page` instance.
Django sees two competing ways to resolve `ArticlePage`:
* `ArticlePage` is a `Page` (due to model inheritance), or
* `ArticlePage` has a separate `Page` instance (due to the page
`OneToOneField`).
The error is caused because Django tries to retrieve the `mtime` field,
which exists on `Page` (inherited via `AbstractPage`). But because
`ArticlePage` also has a `OneToOneField` called `page`, Django gets
confused about how to resolve `mtime`. Instead of treating `page` as a
relationship to another `Page` instance, Django interprets it as a string.
Solutions are either to remove the direct inheritance to `Page` or remove
the `page` field from `AbstractPageType`.
If you have further questions, there are several user support channels
available. Please refer to TicketClosingReasons/UseSupportChannels for
ways to get help.
--
Ticket URL: <https://code.djangoproject.com/ticket/36183#comment:1>
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