fix spatial index creation

Author: timgraham

django_mongodb_backend/gis/schema.py

@@ -3,16 +3,16 @@
 
 
 class GISSchemaEditor:
-    def _field_should_be_indexed(self, model, field):
-        if getattr(field, "spatial_index", False):
-            return True
-        return super()._field_should_be_indexed(model, field)
+    def _create_model_indexes(self, model, column_prefix="", parent_model=None):
+        super()._create_model_indexes(model, column_prefix, parent_model)
+        for field in model._meta.local_fields:
+            if getattr(field, "spatial_index", False):
+                self._add_spatial_index(parent_model or model, field, column_prefix)
 
-    def _add_field_index(self, model, field, *, column_prefix=""):
+    def add_field(self, model, field):
+        super().add_field(model, field)
         if getattr(field, "spatial_index", False):
-            self._add_spatial_index(model, field, column_prefix)
-        else:
-            super()._add_field_index(model, field, column_prefix=column_prefix)
+            self._add_spatial_index(model, field)
 
     def _alter_field(
         self,