made MongoAutoField.get_prep_value() accept ObjectId strings

Author: timgraham

django_mongodb/features.py

@@ -61,15 +61,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "aggregation.tests.AggregateTestCase.test_aggregation_default_passed_another_aggregate",
         "aggregation.tests.AggregateTestCase.test_annotation_expressions",
         "aggregation.tests.AggregateTestCase.test_reverse_fkey_annotate",
-        # MongoAutoField.get_prep_value() must accept strings.
-        "model_forms.test_modelchoicefield.ModelChoiceFieldTests.test_choices",
-        "model_forms.test_modelchoicefield.ModelChoiceFieldTests.test_clean_model_instance",
-        "model_forms.tests.ModelFormBasicTests.test_m2m_editing",
-        "model_forms.tests.ModelMultipleChoiceFieldTests.test_clean_does_deduplicate_values",
-        "model_forms.tests.ModelMultipleChoiceFieldTests.test_model_multiple_choice_field",
-        "model_forms.tests.ModelOneToOneFieldTests.test_onetoonefield",
-        "model_forms.tests.ModelFormBasicTests.test_initial_values",
-        "model_forms.tests.ModelMultipleChoiceFieldTests.test_model_multiple_choice_show_hidden_initial",
         # AutoField (IntegerField) validators crash MongoAutoField.
         "model_forms.tests.ModelFormBasicTests.test_recleaning_model_form_instance",
     }

django_mongodb/fields/auto.py

@@ -15,8 +15,14 @@ def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
 
     def get_prep_value(self, value):
-        # Override AutoField casting to integer.
-        return Field.get_prep_value(self, value)
+        if value is None:
+            return None
+        if isinstance(value, ObjectId):
+            return value
+        try:
+            return ObjectId(value)
+        except errors.InvalidId as e:
+            raise ValueError(f"Field '{self.name}' expected an ObjectId but got {value!r}.") from e
 
     def rel_db_type(self, connection):
         return Field().db_type(connection=connection)