Saving Many To Many data via a modelform in Django

Question

I have a problem saving many to many fields from a form. Here are my models:

class TextIssue(models.Model):
    Issue = models.CharField(max_length=150, unique=True)

    def __unicode__(self):
        return self.Issue

class PadIssue(models.Model):
    Issue = models.CharField(max_length=150, unique=True)

    def __unicode__(self):
        return self.Issue   


class PHIssue(models.Model):
    Data = models.ForeignKey(Data)
    TextIssue = models.ManyToManyField(TextIssue, blank=True, null=True)
    PadIssue = models.ManyToManyField(PadIssue, blank=True, null=True)
    Notes = models.TextField()

    def clean(self):
        from django.core.exceptions import ValidationError
        if self.TextIssue is None and self.PadIssue is None:
            raise ValidationError('You must choose at least one issue category.')   

        if self.Notes is None:
            raise ValidationError('You must write a note regarding the issues selected above.')


class PHIssueForm(ModelForm):

    class Meta:
        model = PHIssue
        exclude = ('Data',)

And here I process the post request in my views.py:

def process_npiform(request, npi_id=None):

    if npi_id:

        try:
            npi = Data.objects.get(id=int(npi_id))
        except: 

            raise Http404   

    if request.method == 'POST':
        data = DataForm(request.POST, instance=npi, prefix='npi_data')

        if data.is_valid():
            update = data.save(commit=False)

            if not request.user.is_superuser:
                update.User = request.user

            update.save()

            if update.Status == 'past-due':

                try:
                    prefab = PHIssue.objects.get(Data=npi)

                except:
                    prefab = PHIssue(Data=Data.objects.get(id=int(update.id)))
                    prefab.save()

                issue = PHIssueForm(request.POST, instance=prefab, prefix='npi_issue')

                if issue.is_valid():

                    save_issue = issue.save(commit=False)

                    save_issue.save()




            return HttpResponseRedirect(reverse('pm'))

        else:
            return render_to_response('npi/data.html', {'data': data, 'issue': issue}, context_instance=RequestContext(request))    
    else:
        return HttpResponseRedirect(reverse('pm'))

Whenever I save through the form, only the Notes text field gets saved in the PHIssue instance, and the many to many fields are left blank. Can someone help me find what is wrong?

Answer 1

http://docs.djangoproject.com/en/dev/topics/forms/modelforms/#the-save-method

When using commit=False, you have to call save_m2m()

m2m relationships require the parent object to be saved first, which you are not doing by using commit=False