How to pass initial parameter to django's ModelForm instance?

Question

The particular case I have is like this:

I have a Transaction model, with fields: from, to (both are ForeignKeys to auth.Use

Answer 1

Use the following method (hopefully it's clear enough):

class BackupForm(ModelForm):
    """Form for adding and editing backups."""

    def __init__(self, *args, **kwargs):
        systemid = kwargs.pop('systemid')
        super(BackupForm, self).__init__(*args, **kwargs)
        self.fields['units'] = forms.ModelMultipleChoiceField(
                required=False,
                queryset=Unit.objects.filter(system__id=systemid),
                widget=forms.SelectMultiple(attrs={'title': _("Add unit")}))

    class Meta:
        model = Backup
        exclude = ('system',)

Create forms like this:

form_backup = BackupForm(request.POST,
                         instance=Backup,
                         systemid=system.id)
form_backup = BackupForm(initial=form_backup_defaults,
                         systemid=system.id)

Hope that helps! Let me know if you need me to explain more in depth.