Question

I have the following models:

class UserProfile(models.Model):
    user = models.ForeignKey(User, unique=True, related_name='profile')
    starred_authors = models.ManyToManyField(Author, related_name='users_with_stars')

class Author(models.Model):
    name = models.CharField(max_length=250)
    slug = models.SlugField(unique=True)

And then in the author template, I would like to show whether or not the currently logged in user has starred that author, but I am running into trouble constructing a suitable query to get this data with the ORM.

In the view I had thought to annotate an author object with a count that will be 0 if the author has not been starred, or 1 if starred. Something like this:

def author_detail(request, slug):
    user_id = request.user.pk
    author = Author.objects.filter(slug=slug).filter(users_with_stars__user__pk=user_id).annotate(fav=Count('users_with_stars'))[0]
    return render_to_response('app/author_detail.html',
                              { 'author': author},
                              context_instance=RequestContext(request)) 

But the above is no good because no objects are found if the current user hasn’t starred the author. What I would like to do is somehow put the last filter inside the annotate, but I haven’t been able to get that working.

Ideally in the template I want to do something like:

{% if author.fav %}
    <p>This is one of your favorite authors</p>
{% endif %}

Any advice is appreciated.

Answer 1

I would probably split this out into a separate property in the template dictionary and calculate it by checking directly whether this user is in the list of users that starred this author.

Something like:

[...]
author = Author.objects.filter(slug=slug)
is_fav = author.users_with_stars.filter(pk=user_id).exists()
return render_to_response('app/author_detail.html',
                          { 'author': author,
                            'is_fav': is_fav },
                          context_instance=RequestContext(request))

And in the template:

{% if is_fav %}
    <p>This is one of your favorite authors</p>
{% endif %}