fix

Author: timgraham

django_mongodb/schema.py

@@ -55,7 +55,7 @@ def add_field(self, model, field):
         if self._field_should_be_indexed(model, field):
             index = Index(fields=[field.name])
             index.name = self._create_index_name(model._meta.db_table, [field.column])
-            self.add_index(model, index)
+            self.add_index(model, index, field=field)
 
     def _alter_field(
         self,
@@ -148,14 +148,19 @@ def alter_index_together(self, model, old_index_together, new_index_together):
     def alter_unique_together(self, model, old_unique_together, new_unique_together):
         pass
 
-    def add_index(self, model, index):
+    def add_index(self, model, index, field=None):
         if index.contains_expressions:
             return
-        idx = IndexModel(
-            [
+        index_orders = (
+            [(field.column, 1)]
+            if field
+            else [
                 (model._meta.get_field(field_name).column, 1 if order == "" else -1)
                 for field_name, order in index.fields_orders
-            ],
+            ]
+        )
+        idx = IndexModel(
+            index_orders,
             name=index.name,
         )
         self.connection.database[model._meta.db_table].create_indexes([idx])