#26163: Wrong related fields in ._meta.get_fields with multiple database on
foreignkey
-------------------------------------+-------------------------------------
Reporter: aRkadeFR | Owner: nobody
Type: Bug | Status: closed
Component: Database layer | Version: 1.9
(models, ORM) |
Severity: Normal | Resolution: invalid
Keywords: models, meta, | Triage Stage:
get_fields, fields, router, | Unreviewed
multiple, databases |
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by charettes):
* status: new => closed
* resolution: => invalid
Comment:
Hi aRkadeFR,
As you might be aware the ORM implements concrete model inheritance using
[https://docs.djangoproject.com/en/1.9/topics/db/models/#multi-table-
inheritance multi-table inheritance] with a unique foreign key
(`OneToOneField`).
In your case a your `GroupA` model could also be explicitly defined as:
{{{#!python
from django.contrib.auth.models import Group
from django.db import models
class GroupA(Group):
group = models.OneToOneField(Group, parent_link=True)
}}}
Given your router definition it looks you're trying to define a cross-
database relation, [https://docs.djangoproject.com/en/1.9/topics/db/multi-
db/#cross-database-relations a feature documented as unsupported]. I can
see you even explicitly tried to work around this limitations by
overriding `allow_relation`.
Without a full traceback it's hard to figure out from where the failure
originates but I suppose a simple `GroupA.object.all()` should fail since
it will be resolved to an SQL query `JOIN`ing the `Group` table.
Now, the `_meta.get_field()` API '''always''' returned inherited fields
from parents so this doesn't look like a bug to me. If you want to make
sure the field is defined on a specific model you should access its
`model` attribute.
If you could provide a full traceback of the exception that was triggered
during the emulated cascade deletion you might be able to get help from
our support channels but given this is documented as unsupported I'll
close the ticket as invalid.
--
Ticket URL: <https://code.djangoproject.com/ticket/26163#comment:2>
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