Question

I have three models:

1. System_Contact
2. System
3. Contact_list

The Contact_List model has two fields: contact and sys and, not surprisingly, is just a manyToMany model to associate a list of contacts to each system. I have modelForm for adding a new contact to the system’s list of contacts:

   class Add_Contact_Form(ModelForm):
       class Meta:
           model = Contact_List
           fields = ('contact',)

Simple, right? My confusion is this: Even thought the Contact_List model has many many duplicate contacts (because one contact can be associated with many systems) each contact is only displayed once within the form’s Select widget.

Why?!

I mean, this is a great default behaviour for my purposes, but I want to make sure this is actually the correct default behaviour that I can rely on, not some random error I have done that just happens to work out for me now.

Answer 1

It’s not that it’s default behaviour, it’s that the select widget in your contact_list form is displaying all of the entries that are from the contact table.

Every model is a table in the database, therefore you have 3 tables:

• ContactTable – where every row in the table is a person
• SystemTable – where every row in the table is a computer (for arguements sake)
• ContactListTable – where every row is a mapping between a system and a list of users

If this is what you are trying to do, you should have the following:

class Contact(models.Model):
    name = ...

class System(models.Model):
    type = ...

class ContactList(models.MOdel):
    system = models.ForeignKey(System)
    contacts = models.ManyToManyField(Contact)

This means that every row in the ContactList table is a relationship between a particular machine from the system table and a list of contacts from the contact table