Question

Ok so this may be really easy for someone else to solve but i’m really confused on how to go about solving this.

So to start, i have a model A that has multiple fields that have many-to-many relationships to specific tables. So for example

class A(models.Model):
    field1 = models.ManyToMany('field1Collection')
    field2 = models.ManyToMany(field2Collection')

class field1Collection(models.Model):
    description = models.TextField()

class field2Collection(models.Model):
    description = models.TextFIeld()

Anyway this is what i’m trying to accomplish. I need to write another model that can hold a ranking system. So for example, i want to create a record where i can define

I have x number of ranks (3 for example):

1. field1Collection Object 3
2. field2Collection Object 6
3. field1Collection Object 2

So i basically want to be able to select objects from my field1Collection and field2Collection tables and assign them ranks. I tried thinking up schemes using foreignkeys and m2m fields but they all go wrong because the model needs to know “ahead” of time which collection set i need to reference. Does this many sense? can anyone help?

Answer 1

You can solve this using GenericForeignKey relationship

from django.db import models
from django.contrib.contenttypes.models import ContentType
from django.contrib.contenttypes import generic

class RankItem(models.Model):
    rank = models.IntegerField()
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')

    def __unicode__(self):
        return self.rank

A normal ForeignKey can only “point to” one other model, which means that if the RankItem model used a ForeignKey it would have to choose one and only one model to store tags for. The contenttypes application provides a special field type which works around this and allows the relationship to be with any model