Ordering of non-model fields in a ModelForm, after #8164

[Marco Bonetti]

After #8164 was closed in [10062], it is not longer possible to define non-model fields in the fields list, as the ordering process raises a KeyError on forms/models.py:166

It would be great if the fields list order could be applied to non-model fields defined in the Form class as well.

[Alex Gaynor]

As I mentioned in IRC, the issue here is not that you can't have extra fields on the Form, it's that you can't use them in the fields ordering option.

[korpios]

fields_for_model is actually the wrong place to be sorting; you want to do that in ModelFormMetaclass.__new__, otherwise you'll miss sorting entirely on fields from declared_fields. Just reassign fields.keyOrder, e.g.:

        if opts.fields:
            fields.keyOrder = [f for f in opts.fields if f in fields.keyOrder]

But, yeah — the changes in r10062 made things go breaky over here. ^_^

[Alex Gaynor]

Nope this works fine(as the test show) since None will get put in the fields_dict and then get reassigned to the new value which doesn't change the ordering.

[Alex Gaynor]

Just to be clear I'm not necessarily saying this is the right place for it, just that it does work. I'm not sure why it would be causing a break for anyone, why do you have fields that aren't on the Model in the fields option?

[Marco Bonetti]

Thank you Alex, your patch worked as expected here.

[Russell Keith-Magee]

(In [10070]) Fixed #10512 -- Corrected the handling of extra fields on a ModelForm?. Thanks to Alex Gaynor for the patch.

[korpios]

Alex: for the sake of ordering them. The fix in r10070 doesn't address that.

[Alex Gaynor]

Yes it does, the behavior of the SortedDict is that on update it doesn't reset the position of the key. So basically what happens is it tries to get a non Model field, it doesn't find it, it puts a None in the fields_dict, then later that gets updated which keeps that key position. And the tests demonstrate this.