[1.10.x] Fixed #26171 -- Made MySQL create an index on ForeignKeys with db_contraint=False.

Refactored "Prevented unneeded index creation on MySQL-InnoDB" (2ceb10f)
to avoid setting db_index=False.

Backport of 6bf7964023487f2a352084e74aca27aecb354d6c from master

2 files changed, 6 insertions, 2 deletions

diff --git a/tests/indexes/models.py b/tests/indexes/models.py
index b348f0365c..dc384ab489 100644
--- a/tests/indexes/models.py
+++ b/tests/indexes/models.py
@@ -19,6 +19,7 @@ class CurrentTranslation(models.ForeignObject):
 class ArticleTranslation(models.Model):
 
     article = models.ForeignKey('indexes.Article', models.CASCADE)
+    article_no_constraint = models.ForeignKey('indexes.Article', models.CASCADE, db_constraint=False)
     language = models.CharField(max_length=10, unique=True)
     content = models.TextField()
 
diff --git a/tests/indexes/tests.py b/tests/indexes/tests.py
index 6e27130f63..dfc503e15d 100644
--- a/tests/indexes/tests.py
+++ b/tests/indexes/tests.py
@@ -62,7 +62,7 @@ class SchemaIndexesTests(TestCase):
     def test_no_index_for_foreignkey(self):
         """
         MySQL on InnoDB already creates indexes automatically for foreign keys.
-        (#14180).
+        (#14180). An index should be created if db_constraint=False (#26171).
         """
         storage = connection.introspection.get_storage_engine(
             connection.cursor(), ArticleTranslation._meta.db_table
@@ -70,4 +70,7 @@ class SchemaIndexesTests(TestCase):
         if storage != "InnoDB":
             self.skip("This test only applies to the InnoDB storage engine")
         index_sql = connection.schema_editor()._model_indexes_sql(ArticleTranslation)
-        self.assertEqual(index_sql, [])
+        self.assertEqual(index_sql, [
+            'CREATE INDEX `indexes_articletranslation_99fb53c2` '
+            'ON `indexes_articletranslation` (`article_no_constraint_id`)'
+        ])