Saving only no fields saves all fields.

[arel]

The issue

I use the pattern of saving only fields that have changed in a model, as such:

obj.save(only=obj.dirty_fields)

However, if the dirty_fields value is an empty list, I would expect save() to save no fields (i.e., be a no-op.) Instead, it saves all the fields, which is counter-intuitive and can lead to problems if I don't explicitly check for an empty list.

I believe the issue is in the line below:

peewee/peewee.py

Line 6521 in ce9375c

if only:

Instead of checking the falseness of only, it might be more appropriate to check if it is None:

 if only is None:
    ...

[coleifer]

Thanks, I've made the change as suggested (although it is if only is not None). Peewee is active-record so calling save with no data will raise a ValueError.