On Sat, 2007-05-19 at 12:02 -0700, [EMAIL PROTECTED] wrote: > > Greetings. I'm trying to get my head wrapped around django, and the > ORM model. So far, I've been pleased with what I've experienced. > However, I'm having some trouble nailing down a couple relations. > > A container can hold (reference) multiple items of the same primary > key. I need a method of storage in the ORM so i can effectively say, > "that container can hold 5 of those items", for example. > > CREATE TABLE items > ( > id SERIAL NOT NULL UNIQUE, > PRIMARY KEY (id) > ); > > CREATE TABLE containers > ( > id SERIAL NOT NULL UNIQUE, > PRIMARY KEY (id) > }; > > CREATE TABLE containers_to_items > ( > container_id INTEGER NOT NULL REFERENCES containers (id), > item_id INTEGER NOT NULL REFERENCES items (id), > item_count INTEGER NOT NULL, > ); > > My attempt at creating a model design is as follows: > > class Item (models.Model): > id = models.AutoField(primary_key=True) > > class Container (models.Model): > id = models.AutoField(primary_key=True) > items = models.ManyToManyField(Item) > > However, this creates the following relation/join table: > > CREATE TABLE whatever_django_labels_it > ( > container_id INTEGER NOT NULL REFERENCES containers (id), > item_id INTEGER NOT NULL REFERENCES items (id), > UNIQUE (container_id, item_id) > ); > > So i need to find out how to model the original relation table field > called item_count, to represent that a container can hold multiple > items, or I need to be able to drop the django-imposed UNIQUE > constraint so I can add multiple identical item_id values for a single > container_id value: > > INSERT INTO whatever_django_labels_it (container_id, item_id) VALUES > (1, 1); > INSERT INTO whatever_django_labels_it (container_id, item_id) VALUES > (1, 1); > INSERT INTO whatever_django_labels_it (container_id, item_id) VALUES > (1, 1); > > etc > > Input?
Any time when you want to put extra fields on the intermediary table of a many-to-many relationship, you need to model that table explicitly and use a couple of ForeignKey fields to set up the relationship. See http://www.djangoproject.com/documentation/models/m2m_intermediary/ for an example. Regards, Malcolm --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
