fix deferral of foreign key fields

Author: timgraham

.github/workflows/test-python.yml

@@ -69,6 +69,7 @@ jobs:
           python3 django_repo/tests/runtests.py --settings mongodb_settings -v 2
           basic
           empty
+          defer.tests.DeferTests.test_only_values_does_not_defer
           from_db_value
           lookup.tests.LookupTests.test_escaping
           model_fields

django_mongodb/query.py

@@ -129,7 +129,7 @@ def delete(self):
     def get_cursor(self):
         if self.query.low_mark == self.query.high_mark:
             return []
-        fields = [col.field.name for col in self.columns] if self.columns else None
+        fields = [col.target.column for col in self.columns] if self.columns else None
         cursor = self.collection.find(self.mongo_query, fields)
         if self.ordering:
             cursor.sort(self.ordering)