Question

Im using the below code in my views.py page to render a html page. This piece of code is from a Django book and im trying to understand the bookmark_set attribute.

views.py

def user_page(request, username):
    try:
        user = User.objects.get(username=username)
    except User.DoesNotExist:
        raise Http404(u'Requested user not found')

    bookmarks = user.bookmark_set.all()

    template = get_template('user_page.html')

    variables = Context({'username':username, 'bookmarks':bookmarks})

    output = template.render(variables)
    return HttpResponse(output)

models.py

from django.db import models
from django.contrib.auth.models import User

class Link(models.Model):
    url = models.URLField(unique=True)

class Bookmark(models.Model):
    title = models.CharField(max_length=200)
    user  = models.ForeignKey(User)
    link  = models.ForeignKey(Link)

When I run this piece of code in my Python shell, I get the following error

from django.contrib.auth.models import User
from bookmarks.models import *
user=User.object.get(id=1)
user.bookmark_set.all()

Attribute Error: ‘User’ object has no attribute ‘bookmark_set’

Why do I get this error?

How does the set attribute of the User work?

Answer 1

The bookmark_set attribute provides a convenient way to traverse the reverse relationship, i.e. to get all of a user’s bookmarks. You can read more about it in the docs:

Django also creates API accessors for the “other” side of the relationship — the link from the related model to the model that defines the relationship. For example, a Blog object b has access to a list of all related Entry objects via the entry_set attribute: b.entry_set.all().

You can actually specify the name of the reverse relationship attribute by providing a related_name in your model:

class Bookmark(models.Model):
    user  = models.ForeignKey(User, related_name="bookmarks")

$ myuser.bookmarks.all()

Have you definitely created your models in the DB by running python manage.py syncdb? It looks like you are doing everything correctly