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
26163	Wrong related fields in ._meta.get_fields with multiple database on foreignkey	aRkadeFR	nobody	"Hello,

I tried to find a similar ticket and didn't find it.

I setup a simple use case to show the error.
2 applications: appa and appb.

You override (by inheritance) django.contrib.auth.models.Group in <appa>, you have a model ModelB in <appb> that has a foreign key to Group of django.contrib.auth.
You setup a DatabaseRouter to route every <appa> model to the 'default' database, and all <appb> model to the 'other' database.

If you ._meta.get_fields() on GroupA, you see the foreign key of the ModelB which is related to django.contrib.auth in the other database. The related field shouldn't be visible from the get_fields() on GroupA.

I got this error from debugging a ""missing attribute"" while Django was emulating the DELETE ON_CASCADE in python and following the wrong parent model to get then the related_fields.

Thanks for all the information and keep up the good work :)

{{{
# settings
DATABASE_ROUTERS = ['projecta.router.CustomRouter']
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'HOST': 'localhost',
        'PORT': '5432',
        'NAME': 'default',
        'USER': 'postgres_user',
        'PASSWORD': 'pouetpouet',
    },
    'other': {
        'ENGINE': 'django.db.backends.postgresql_psycopg2',
        'HOST': 'localhost',
        'PORT': '5432',
        'NAME': 'other',
        'USER': 'postgres_user',
        'PASSWORD': 'pouetpouet',
    }
}


# projecta/router.py
class CustomRouter(object):
    """""" CustomRouter """"""
    def db_for_read(self, model, **hints):
        if model._meta.app_label == 'appb':
            return 'other'
        if model._meta.app_label == 'auth':
            return 'other'
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label == 'appb':
            return 'other'
        if model._meta.app_label == 'auth':
            return 'other'
        return None

    def allow_relation(self, obj1, obj2, **hints):
        if obj1._meta.app_label == 'auth' or \
           obj2._meta.app_label == 'auth':
            return True
        return None

    def allow_migrate(self, db, app_label, model=None, **hints):
        """""" auth need to go to the other database (for projectb) """"""
        if app_label == 'appa':
            return db == 'default'
        if app_label == 'appb':
            return db == 'other'
        return None


# appa/models.py
from django.contrib.auth.models import Group
from django.db import models

class GroupA(Group):
    extra_field = models.IntegerField()

# appb/models.py
from django.contrib.auth.models import Group

class ModelB(models.Model):
    group = models.ForeignKey(Group, null=False)


# ipython
In [3]: GroupA._meta.get_fields()
Out[3]: 
(<ManyToManyRel: auth.user>,
 <ManyToOneRel: projectb.modelb>,
<...>
}}}"	Bug	closed	Database layer (models, ORM)	1.9	Normal	invalid	models, meta, get_fields, fields, router, multiple, databases		Unreviewed	0	0	0	0	0	0