Document that using ModelAdmin.list_filter with foreign keys may require a database router

[Adam Brenecki]

I'm using Django's admin on a model on one of a number of secondary databases. The model has managed = False and doesn't exist on the default database. I'm not using a custom database router; I've overridden methods on my ModelAdmin as per here: ​https://docs.djangoproject.com/en/1.11/topics/db/multi-db/#exposing-multiple-databases-in-django-s-admin-interface. This mostly works, except when I add a ForeignKey field to list_filter, when it appears to try to query the primary database for the values to display in the filter, and I can't find a way to override this behaviour in ModelAdmin.

This happens both on Django 1.11.5 and on master (as of commit 1b73ccc); other models that have list_filters that aren't foreign keys work fine, as does this model if I comment out the line with list_filter.

Below is an excerpt from my admin.py as well as the full stack trace:

from django.contrib import admin

from . import models


class ApplyOLModelAdmin(admin.ModelAdmin):
    def save_model(self, request, obj, form, change):
        obj.save(using=request.applyol)

    def delete_model(self, request, obj):
        obj.delete(using=request.applyol)

    def get_queryset(self, request):
        return super().get_queryset(request).using(request.applyol)

    def formfield_for_foreignkey(self, db_field, request, **kwargs):
        return super().formfield_for_foreignkey(
            db_field, request, using=request.applyol, **kwargs
        )

    def formfield_for_manytomany(self, db_field, request, **kwargs):
        return super().formfield_for_manytomany(
            db_field, request, using=request.applyol, **kwargs
        )

    def has_module_permission(self, request):
        return True

    def has_add_permission(self, request, obj=None):
        return True

    def has_change_permission(self, request, obj=None):
        return True

    def has_delete_permission(self, request, obj=None):
        return True


@admin.register(models.CountryCity)
class CountryCityAdmin(ApplyOLModelAdmin):
    list_display = ('country', 'code', 'name')
    list_display_links = ('name',)
    list_filter = ('country',)
    ordering = ('country__name', 'name')

Environment:


Request Method: GET
Request URL: http://localhost:8000/dev/admin/applyol_editor/countrycity/

Django Version: 2.1.dev20171016175638
Python Version: 3.6.2
Installed Applications:
('sl_admin.apps.applyol_editor',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'form_utils',
 'webpack_loader',
 'widget_tweaks',
 'sl_admin.lib',
 'sl_admin.apps.accounts',
 'sl_admin.apps.landing',
 'sl_admin.apps.form_builder')
Installed Middleware:
('django.middleware.security.SecurityMiddleware',
 'whitenoise.middleware.WhiteNoiseMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'csp.middleware.CSPMiddleware',
 'sl_admin.lib.middleware.XUACompatibleMiddleware',
 'sl_admin.apps.accounts.middleware.SocialAuthErrorMiddleware',
 'sl_admin.lib.environment.EnvironmentMiddleware',
 'rollbar.contrib.django.middleware.RollbarNotifierMiddleware')



Traceback:

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in _execute
  86.                 return self.cursor.execute(sql, params)

The above exception (relation "APPLYOL.TBLCOUNTRY" does not exist
LINE 1: ...ODE", "APPLYOL"."TBLCOUNTRY"."ISNATIONALITY" FROM "APPLYOL"....
                                                             ^
) was the direct cause of the following exception:

File "/Users/adambrenecki/Projects/django/django/core/handlers/exception.py" in inner
  35.             response = get_response(request)

File "/Users/adambrenecki/Projects/django/django/core/handlers/base.py" in _get_response
  128.                 response = self.process_exception_by_middleware(e, request)

File "/Users/adambrenecki/Projects/django/django/core/handlers/base.py" in _get_response
  126.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/options.py" in wrapper
  574.                 return self.admin_site.admin_view(view)(*args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/utils/decorators.py" in _wrapped_view
  142.                     response = view_func(request, *args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/views/decorators/cache.py" in _wrapped_view_func
  44.         response = view_func(request, *args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/sites.py" in inner
  223.             return view(request, *args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/utils/decorators.py" in _wrapper
  62.             return bound_func(*args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/utils/decorators.py" in _wrapped_view
  142.                     response = view_func(request, *args, **kwargs)

File "/Users/adambrenecki/Projects/django/django/utils/decorators.py" in bound_func
  58.                 return func.__get__(self, type(self))(*args2, **kwargs2)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/options.py" in changelist_view
  1570.             cl = self.get_changelist_instance(request)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/options.py" in get_changelist_instance
  705.             self,

File "/Users/adambrenecki/Projects/django/django/contrib/admin/views/main.py" in __init__
  75.         self.queryset = self.get_queryset(request)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/views/main.py" in get_queryset
  313.          filters_use_distinct) = self.get_filters(request)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/views/main.py" in get_filters
  129.                         self.model, self.model_admin, field_path=field_path

File "/Users/adambrenecki/Projects/django/django/contrib/admin/filters.py" in create
  157.             return list_filter_class(field, request, params, model, model_admin, field_path=field_path)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/filters.py" in __init__
  168.         self.lookup_choices = self.field_choices(field, request, model_admin)

File "/Users/adambrenecki/Projects/django/django/contrib/admin/filters.py" in field_choices
  195.         return field.get_choices(include_blank=False)

File "/Users/adambrenecki/Projects/django/django/db/models/fields/__init__.py" in get_choices
  812.                        limit_choices_to)]

File "/Users/adambrenecki/Projects/django/django/db/models/query.py" in __iter__
  270.         self._fetch_all()

File "/Users/adambrenecki/Projects/django/django/db/models/query.py" in _fetch_all
  1174.             self._result_cache = list(self._iterable_class(self))

File "/Users/adambrenecki/Projects/django/django/db/models/query.py" in __iter__
  55.         results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)

File "/Users/adambrenecki/Projects/django/django/db/models/sql/compiler.py" in execute_sql
  1043.             cursor.execute(sql, params)

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in execute
  101.             return super().execute(sql, params)

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in execute
  69.         return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in _execute_with_wrappers
  78.         return executor(sql, params, many, context)

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in _execute
  86.                 return self.cursor.execute(sql, params)

File "/Users/adambrenecki/Projects/django/django/db/utils.py" in __exit__
  89.                 raise dj_exc_value.with_traceback(traceback) from exc_value

File "/Users/adambrenecki/Projects/django/django/db/backends/utils.py" in _execute
  86.                 return self.cursor.execute(sql, params)

Exception Type: ProgrammingError at /dev/admin/applyol_editor/countrycity/
Exception Value: relation "APPLYOL.TBLCOUNTRY" does not exist
LINE 1: ...ODE", "APPLYOL"."TBLCOUNTRY"."ISNATIONALITY" FROM "APPLYOL"....
                                                             ^

[Tomer Chachamu]

Yep, that's an oversight in the documentation. However, you can remove the admin customisation and write a database router instead. That will work not just for the admin but throughout your website too. If you are setting request.applyol in middleware, you can in the same middleware tell your database router to change the database that it should give for db_for_read(model=ApplyOl). Here's an example you can adapt: ​https://github.com/yandex/django_replicated/blob/master/django_replicated/router.py

[Tim Graham]

Absent another proposal, it sounds like documenting that a database router is required for this case could be a solution.