splitting a ManyToManyField over multiple form fields in a ModelForm

Question

So I have a model with a ManyToManyField called tournaments. I have a ModelForm with two tournament fields:

pay_tourns = forms.ModelMultipleChoiceField(
                        queryset=Tourn.objects.all().active().pay_tourns(),
                        widget=forms.CheckboxSelectMultiple())
rep_tourns = forms.ModelMultipleChoiceField(
                        queryset=Tourn.objects.all().active().rep_tourns(),
                        widget=forms.CheckboxSelectMultiple())

The methods after all() there are from a subclassed QuerySet. When I'm saving the form in my view I do thus:

post.tournaments = (post_form.cleaned_data.get('pay_tourns')
                                + post_form.cleaned_data.get('rep_tourns'))

Anyway, this all works fine. What I can't figure out how to do is fill these form fields out when I'm loading an existing post. That is, when I pass instance=post to the form. Any ideas?

Answer 1

You could do something like this to the ModelForm:

def __init__(self, *args, **kwargs):
    super(MyForm, self).__init__(*args, **kwargs)

    instance = kwargs.get('instance')
    if instance:
        self.fields['pay_tourns'].queryset.filter(post=instance)
        self.fields['rep_tourns'].queryset.filter(post=instance)

I don't see why that wouldn't work, but I'm going to test it just to make sure...

EDIT: Tested and it works.

Answer 2

Paolo Bergantino was on the right track, and helped me find it. This was the solution:

def __init__(self, *args, **kwargs):
    super(MyForm, self).__init__(*args, **kwargs)

    instance = kwargs.get('instance')
    if instance:
        self.fields['pay_tourns'].initial = [ o.id for o in instance.tournaments.all().active().pay_tourns()]
        self.fields['rep_tourns'].initial = [ o.id for o in instance.tournaments.all().active().rep_tourns()]