ModelMultipleChoiceField, clean and to_python

[Matt Hoskins]

The validation documentation for forms says that to_python on the form field is the first step in validation. I've written some code (the details of which don't really matter) which makes use of to_python on fields in doing so I discovered that "to_python" on ModelMultipleChoiceField doesn't work. The reason for this is that ModelMultipleChoiceField inherits from ModelChoiceField but then puts everything into "clean" and doesn't do anything about "to_python".

I would guess it was quicker/easier to put everything together in "clean" when the method was originally authored?

Given "to_python" is documented in forms as being a first step it feels to me untidy, at least, that this "to_python" is hanging around on ModelMultipleChoiceField in a non-working state and also that everything is put into "clean" - it would feel tidier to move the "to_python"-ish parts of ModelMultipleChoiceField out of "clean" and into "to_python". I also wonder if the "required" and "invalid_choice" tests from "clean" ought to be put into a "validate" method to make it consistent with how other fields behave, although I note from ModelChoiceField that an invalid choice cannot be converted to python since an instance can't be found for it so maybe to_python is the appropriate place for the invalid_choice test at least! I describe as "untidy" rather than as a bug as I'm not clear whether the documentation on validation is suggesting fields should have a "to_python" method and/or whether it's reasonable to expect "to_python" methods (if they exist) on form fields should work.

Worth me raising this as a ticket? Or is it a non-issue or there's a valid reason for keeping things as they are in ModelMultipleChoiceField's clean method?

Matt