Refs #24299 -- Made contenttypes migrations signal handler more robust.

django/contrib/contenttypes/models.py

@@ -4,7 +4,7 @@ import warnings
 
 from django.apps import apps
 from django.db import models
-from django.db.utils import OperationalError, ProgrammingError
+from django.db.utils import IntegrityError, OperationalError, ProgrammingError
 from django.utils.deprecation import RemovedInDjango20Warning
 from django.utils.encoding import force_text, python_2_unicode_compatible
 from django.utils.translation import ugettext_lazy as _
@@ -58,18 +58,11 @@ class ContentTypeManager(models.Manager):
 
         # The ContentType entry was not found in the cache, therefore we
         # proceed to load or create it.
+        try:
             try:
                 # We start with get() and not get_or_create() in order to use
                 # the db_for_read (see #20401).
                 ct = self.get(app_label=opts.app_label, model=opts.model_name)
-        except (OperationalError, ProgrammingError):
-            # It's possible to migrate a single app before contenttypes,
-            # as it's not a required initial dependency (it's contrib!)
-            # Have a nice error for this.
-            raise RuntimeError(
-                "Error creating new content types. Please make sure contenttypes "
-                "is migrated before trying to migrate apps individually."
-            )
             except self.model.DoesNotExist:
                 # Not found in the database; we proceed to create it.  This time we
                 # use get_or_create to take care of any race conditions.
@@ -77,6 +70,14 @@ class ContentTypeManager(models.Manager):
                     app_label=opts.app_label,
                     model=opts.model_name,
                 )
+        except (OperationalError, ProgrammingError, IntegrityError):
+            # It's possible to migrate a single app before contenttypes,
+            # as it's not a required initial dependency (it's contrib!)
+            # Have a nice error for this.
+            raise RuntimeError(
+                "Error creating new content types. Please make sure contenttypes "
+                "is migrated before trying to migrate apps individually."
+            )
         self._add_to_cache(self.db, ct)
         return ct
 

django/contrib/contenttypes/tests/tests.py

@@ -5,8 +5,9 @@ import warnings
 from django.contrib.contenttypes.models import ContentType
 from django.contrib.contenttypes.views import shortcut
 from django.contrib.sites.shortcuts import get_current_site
+from django.db.utils import IntegrityError, OperationalError, ProgrammingError
 from django.http import Http404, HttpRequest
-from django.test import TestCase, override_settings
+from django.test import TestCase, mock, override_settings
 from django.utils import six
 
 from .models import (
@@ -264,3 +265,26 @@ class ContentTypesTests(TestCase):
             "ContentType.name field doesn't exist any longer. Please remove it from your code."
         )
         self.assertTrue(ContentType.objects.filter(model='OldModel').exists())
+
+    @mock.patch('django.contrib.contenttypes.models.ContentTypeManager.get_or_create')
+    @mock.patch('django.contrib.contenttypes.models.ContentTypeManager.get')
+    def test_message_if_get_for_model_fails(self, mocked_get, mocked_get_or_create):
+        """
+        Check that `RuntimeError` with nice error message is raised if
+        `get_for_model` fails because of database errors.
+        """
+
+        def _test_message(mocked_method):
+            for ExceptionClass in (IntegrityError, OperationalError, ProgrammingError):
+                mocked_method.side_effect = ExceptionClass
+                with self.assertRaisesMessage(
+                    RuntimeError,
+                    "Error creating new content types. Please make sure contenttypes "
+                    "is migrated before trying to migrate apps individually."
+                ):
+                    ContentType.objects.get_for_model(ContentType)
+
+        _test_message(mocked_get)
+
+        mocked_get.side_effect = ContentType.DoesNotExist
+        _test_message(mocked_get_or_create)