Class-based views for M2M relationship with intermediate model

Question

I have a M2M relationship between two Models which uses an intermediate model. For the sake of discussion, let\'s use the example from the manual:

class Pers         


        

Answer 1

I was facing pretty the same problem just a few days ago. Django has problems to process intermediary m2m relationships.

This is the solutions what I have found useful:

1. Define new CreateView
class GroupCreateView(CreateView):
    form_class = GroupCreateForm
    model = Group
    template_name = 'forms/group_add.html'
    success_url = '/thanks'

Then alter the save method of defined form - GroupCreateForm. Save is responsible for making changes permanent to DB. I wasn't able to make this work just through ORM, so I've used raw SQL too:

1. Define new CreateView
class GroupCreateView(CreateView):


class GroupCreateForm(ModelForm):
    def save(self):
        # get data from the form
        data = self.cleaned_data
        cursor = connection.cursor()
        # use raw SQL to insert the object (in your case Group)
        cursor.execute("""INSERT INTO group(group_id, name)
                          VALUES (%s, %s);""" (data['group_id'],data['name'],))
        #commit changes to DB
        transaction.commit_unless_managed()
        # create m2m relationships (using classical object approach)
        new_group = get_object_or_404(Group, klient_id = data['group_id'])
        #for each relationship create new object in m2m entity
        for el in data['members']:
            Membership.objects.create(group = new_group, membership = el)
        # return an object Group, not boolean!
        return new_group

Note:I've changed the model a little bit, as you can see (i have own unique IntegerField for primary key, not using serial. That's how it got into get_object_or_404