Question

I have two models

class Friend(models.Model):
       me = models.ForeignKey(User)
       friend = models.ForeignKey(User)
       remark = models.CharField(max_length=15)

      def __unicode__(self):
            return self.remark

class Message(models.Model):
       from_user = models.ForeignKey(User)
       to_user = models.ForeignKey(User)
       ...

I make a form for Message

class MessageForm(ModelForm):
        class Meta:
              model = Message

but when i display the form in html, i hope i display to_user’s choice list just by ‘remark’ ( in Friend model)

and I override MessageForm ‘s init method like follow:

class MessageForm(ModelForm):
        class Meta:
              model = Message
        def __init__(self,*args,**kwargs):
              super(MessageForm, self).__init__(*args,**kwargs)
              init = kwargs.get('initial')
              if init:
                  if 'from_user' in init:
                       me = init['from_user']
                       self.fields['to_user'].queryset = Friend.objects.filter(me=me)

well when the data post, the form.is_valid() raise error : Cannot assign “”: “Message.to_user” must be a “User” instance.

so i want to change self.fields[‘to_user’] ‘s value before is_valid() is call like:

def is_valid(self):
     # do something  to fix the problem
     super(MessageForm, self).is_valid()

Answer 1

is_valid() calls the clean() method of the form, so put your hack in there:

def clean(self):
    # hack hack hack, operating on self.cleaned_data

    return self.cleaned_data