remove GeometryField in _alter_field()

Author: timgraham

django_mongodb_backend_gis/schema.py

@@ -1,4 +1,3 @@
-from django.contrib.gis.db.models import GeometryField
 from pymongo import GEOSPHERE
 from pymongo.operations import IndexModel
 
@@ -38,9 +37,8 @@ def _alter_field(
             new_db_params,
             strict=strict,
         )
-
-        old_field_spatial_index = isinstance(old_field, GeometryField) and old_field.spatial_index
-        new_field_spatial_index = isinstance(new_field, GeometryField) and new_field.spatial_index
+        old_field_spatial_index = getattr(old_field, "spatial_index", False)
+        new_field_spatial_index = getattr(new_field, "spatial_index", False)
         if not old_field_spatial_index and new_field_spatial_index:
             self._add_spatial_index(model, new_field)
         elif old_field_spatial_index and not new_field_spatial_index: