ModelChoiceField/ModelMultipleChoiceField.clean() should catch ValidationError raised by the queryset operations

[Tim Graham]

As seen in cdc25ac4747bf5a6cdc2e70461c2d43c54529d35, ValueError and TypeError are caught by the queryset operations in ModelChoiceField.clean() and ModelMultipleChoiceField.clean(), however, these exceptions are particular to ​IntegerFielld.get_prep_value(). A more common implementation of get_prep_value() delegates to to_python() which is supposed to raise ValidationError for invalid values (​as seen in UUIDField). Thus, ValidationError should also be caught so that the ​invalid choice error is raised rather than the "invalid" error of the model field.

Aside: I discovered this while implementing ObjectIdAutoField in django-mongodb-backend. I had some difficulty figuring out what exception get_prep_value() should raise. I have to do some more digging to understand if IntegerFielld.get_prep_value() raising ValueError and TypeError is really appropriate, but this is the subject of another ticket.

[Sarah Boyce]

Thank you! Confirmed this is inconsistently handled. The following test fails for example:

tests/model_forms/tests.py

@@ -74 +74 @@
     WriterProfile,
     temp_storage_dir,
     test_images,
+    UUIDPK,
 )
 
 if test_images:
@@ -2177 +2178 @@
         with self.assertRaises(ValidationError):
             f.clean([c6.id])
 
+    def test_model_multiple_choice_invalid_pk_value_error_messages(self):
+        uuid_f = forms.ModelMultipleChoiceField(UUIDPK.objects.all())
+        f = forms.ModelMultipleChoiceField(Category.objects.all())
+        for model_multiple_choice_form in [f, uuid_f]:
+            with self.assertRaisesMessage(
+                ValidationError,
+                "“invalid” is not a valid value."
+            ):
+                model_multiple_choice_form.clean(["invalid"])
+
     def test_model_multiple_choice_required_false(self):