Fixed #30673 -- Relaxed system check for db_table collision when database routers are installed by turning the error into a warning.

AUTHORS

@@ -18,6 +18,7 @@ answer newbie questions, and generally made Django that much better:
     Adam Malinowski <https://adammalinowski.co.uk/>
     Adam Vandenberg
     Adiyat Mubarak <adiyatmubarak@gmail.com>
+    Adnan Umer <u.adnan@outlook.com>
     Adrian Holovaty <adrian@holovaty.com>
     Adrien Lemaire <lemaire.adrien@gmail.com>
     Afonso Fernández Nogueira <fonzzo.django@gmail.com>

django/core/checks/model_checks.py

@@ -4,7 +4,8 @@ from collections import defaultdict
 from itertools import chain
 
 from django.apps import apps
-from django.core.checks import Error, Tags, register
+from django.conf import settings
+from django.core.checks import Error, Tags, Warning, register
 
 
 @register(Tags.models)
@@ -35,14 +36,25 @@ def check_all_models(app_configs=None, **kwargs):
             indexes[model_index.name].append(model._meta.label)
         for model_constraint in model._meta.constraints:
             constraints[model_constraint.name].append(model._meta.label)
+    if settings.DATABASE_ROUTERS:
+        error_class, error_id = Warning, 'models.W035'
+        error_hint = (
+            'You have configured settings.DATABASE_ROUTERS. Verify that %s '
+            'are correctly routed to separate databases.'
+        )
+    else:
+        error_class, error_id = Error, 'models.E028'
+        error_hint = None
     for db_table, model_labels in db_table_models.items():
         if len(model_labels) != 1:
+            model_labels_str = ', '.join(model_labels)
             errors.append(
-                Error(
+                error_class(
                     "db_table '%s' is used by multiple models: %s."
-                    % (db_table, ', '.join(db_table_models[db_table])),
+                    % (db_table, model_labels_str),
                     obj=db_table,
-                    id='models.E028',
+                    hint=(error_hint % model_labels_str) if error_hint else None,
+                    id=error_id,
                 )
             )
     for index_name, model_labels in indexes.items():

docs/ref/checks.txt

@@ -317,6 +317,8 @@ Models
   or a number.
 * **models.E034**: The index name ``<index>`` cannot be longer than
   ``<max_length>`` characters.
+* **models.W035**: ``db_table`` ``<db_table>`` is used by multiple models:
+  ``<model list>``.
 
 Security
 --------

docs/releases/2.2.5.txt

@@ -9,4 +9,6 @@ Django 2.2.5 fixes several bugs in 2.2.4.
 Bugfixes
 ========
 
-* ...
+* Relaxed the system check added in Django 2.2 for models to reallow use of the
+  same ``db_table`` by multiple models when database routers are installed
+  (:ticket:`30673`).

tests/check_framework/test_model_checks.py

@@ -1,12 +1,16 @@
 from django.core import checks
-from django.core.checks import Error
+from django.core.checks import Error, Warning
 from django.db import models
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
 from django.test.utils import (
-    isolate_apps, modify_settings, override_system_checks,
+    isolate_apps, modify_settings, override_settings, override_system_checks,
 )
 
 
+class EmptyRouter:
+    pass
+
+
 @isolate_apps('check_framework', attr_name='apps')
 @override_system_checks([checks.model_checks.check_all_models])
 class DuplicateDBTableTests(SimpleTestCase):
@@ -28,6 +32,30 @@ class DuplicateDBTableTests(SimpleTestCase):
             )
         ])
 
+    @override_settings(DATABASE_ROUTERS=['check_framework.test_model_checks.EmptyRouter'])
+    def test_collision_in_same_app_database_routers_installed(self):
+        class Model1(models.Model):
+            class Meta:
+                db_table = 'test_table'
+
+        class Model2(models.Model):
+            class Meta:
+                db_table = 'test_table'
+
+        self.assertEqual(checks.run_checks(app_configs=self.apps.get_app_configs()), [
+            Warning(
+                "db_table 'test_table' is used by multiple models: "
+                "check_framework.Model1, check_framework.Model2.",
+                hint=(
+                    'You have configured settings.DATABASE_ROUTERS. Verify '
+                    'that check_framework.Model1, check_framework.Model2 are '
+                    'correctly routed to separate databases.'
+                ),
+                obj='test_table',
+                id='models.W035',
+            )
+        ])
+
     @modify_settings(INSTALLED_APPS={'append': 'basic'})
     @isolate_apps('basic', 'check_framework', kwarg_name='apps')
     def test_collision_across_apps(self, apps):
@@ -50,6 +78,34 @@ class DuplicateDBTableTests(SimpleTestCase):
             )
         ])
 
+    @modify_settings(INSTALLED_APPS={'append': 'basic'})
+    @override_settings(DATABASE_ROUTERS=['check_framework.test_model_checks.EmptyRouter'])
+    @isolate_apps('basic', 'check_framework', kwarg_name='apps')
+    def test_collision_across_apps_database_routers_installed(self, apps):
+        class Model1(models.Model):
+            class Meta:
+                app_label = 'basic'
+                db_table = 'test_table'
+
+        class Model2(models.Model):
+            class Meta:
+                app_label = 'check_framework'
+                db_table = 'test_table'
+
+        self.assertEqual(checks.run_checks(app_configs=apps.get_app_configs()), [
+            Warning(
+                "db_table 'test_table' is used by multiple models: "
+                "basic.Model1, check_framework.Model2.",
+                hint=(
+                    'You have configured settings.DATABASE_ROUTERS. Verify '
+                    'that basic.Model1, check_framework.Model2 are correctly '
+                    'routed to separate databases.'
+                ),
+                obj='test_table',
+                id='models.W035',
+            )
+        ])
+
     def test_no_collision_for_unmanaged_models(self):
         class Unmanaged(models.Model):
             class Meta: