add logic to include deleting _meta.indexes to _delete_indexes (#292)

Author: mShan0

mssql/schema.py

@@ -313,7 +313,7 @@ def _alter_field(self, model, old_field, new_field, old_type, new_type,
         if (old_is_auto and not new_is_auto) or (not old_is_auto and new_is_auto):
             raise NotImplementedError("the backend doesn't support altering from %s to %s." %
                 (old_field.get_internal_type(), new_field.get_internal_type()))
-        
+
         # Drop any FK constraints, we'll remake them later
         fks_dropped = set()
         if old_field.remote_field and old_field.db_constraint:
@@ -788,11 +788,23 @@ def _delete_indexes(self, model, old_field, new_field):
             if old_field.column in columns:
                 index_columns.append(columns)
 
+        for index in model._meta.indexes:
+            columns = [model._meta.get_field(field).column for field in index.fields]
+            if old_field.column in columns:
+                index_columns.append(columns)
+
         for fields in model._meta.unique_together:
             columns = [model._meta.get_field(field).column for field in fields]
             if old_field.column in columns:
                 index_columns.append(columns)
         if index_columns:
+            # remove duplicates first
+            temp = []
+            for columns in index_columns:
+                if columns not in temp:
+                    temp.append(columns)
+            index_columns = temp
+
             for columns in index_columns:
                 index_names = self._constraint_names(model, columns, index=True)
                 for index_name in index_names: