Fixed #14180 -- Prevented unneeded index creation on MySQL-InnoDB

Thanks zimnyx for the report and Simon Charette, Tim Graham for
the reviews.

1 files changed, 12 insertions, 0 deletions

diff --git a/django/db/backends/mysql/schema.py b/django/db/backends/mysql/schema.py
index 573779a49b..697490e888 100644
--- a/django/db/backends/mysql/schema.py
+++ b/django/db/backends/mysql/schema.py
@@ -51,3 +51,15 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
                 'table': self.quote_name(model._meta.db_table),
                 'column': self.quote_name(field.column),
             }, [effective_default])
+
+    def _model_indexes_sql(self, model):
+        storage = self.connection.introspection.get_storage_engine(
+            self.connection.cursor(), model._meta.db_table
+        )
+        if storage == "InnoDB":
+            for field in model._meta.local_fields:
+                if field.db_index and not field.unique and field.get_internal_type() == "ForeignKey":
+                    # Temporary setting db_index to False (in memory) to disable
+                    # index creation for FKs (index automatically created by MySQL)
+                    field.db_index = False
+        return super(DatabaseSchemaEditor, self)._model_indexes_sql(model)