Add Field.value_is_model_instance

Author: timgraham

django_mongodb_backend/compiler.py

@@ -746,7 +746,7 @@ def execute_sql(self, result_type):
             elif hasattr(value, "prepare_database_save"):
                 if field.remote_field:
                     value = value.prepare_database_save(field)
-                elif not hasattr(field, "embedded_model"):
+                elif not getattr(field, "value_is_model_instance", False):
                     raise TypeError(
                         f"Tried to update field {field} with a model "
                         f"instance, {value!r}. Use a value compatible with "

django_mongodb_backend/fields/embedded_model.py

@@ -12,6 +12,8 @@
 class EmbeddedModelField(models.Field):
     """Field that stores a model instance."""
 
+    value_is_model_instance = True
+
     def __init__(self, embedded_model, *args, **kwargs):
         """
         `embedded_model` is the model class of the instance to be stored.

django_mongodb_backend/fields/embedded_model_array.py

@@ -13,6 +13,8 @@
 
 
 class EmbeddedModelArrayField(ArrayField):
+    value_is_model_instance = True
+
     def __init__(self, embedded_model, **kwargs):
         if "size" in kwargs:
             raise ValueError("EmbeddedModelArrayField does not support size.")