Django, getting related objects in a loop of objects

Question

Let's say users can make a list of Types. When they add to their list of types, a new UserType object is created with the User and the Type as ForeignKeys.

Other users can 'like' the individual types that a user has listed (UserTypes).

Given that I query for a user's UserTypes, how can I best get the number of UserLikes on each UserType in a QuerySet to use in a template? Would I simply loop through, query each and return the result as a separate list? That seems pretty messy.

class Type(model.Models):
    name = models.CharField(max_length=100, blank=False)
    description = models.TextField(max_length=1000, blank=True)
    created_by = models.ForeignKey(User, blank=True, null=True, unique=False)


class UserType(model.Models):
    user = models.ForeignKey(User, unique=False)
    type = models.ForeignKey(Type, unique=False)
    is_active = models.BooleanField(default=True)


class UserLike(model.Models):
    user = models.ForeignKey(User, unique=False)
    user_type = models.ForeignKey(UserType, unique=False)

Fiver · Accepted Answer · 2013-08-16 02:43:32Z

1

How about a simple count of the UserLike set for the UserType instance:

some_user_type = UserType.objects.get(user_id=some_user_pk)
like_count = some_user_type.userlike_set.all().count()

or if you have a bunch of UserTypes in a queryset you can use annotate:

from django.db.models import Count
qs = UserType.objects.annotate(Count('userlike'))

Now each result in the queryset has the count: qs[0].userlike__count

edited Aug 16, 2013 at 2:43

answered Aug 16, 2013 at 2:30

Fiver

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3 Comments

aroooo Over a year ago

This would return one UserType that belongs to the User and count the likes on it. I'm trying to get all UserLikes given a QuerySet of UserTypes to be used in my template.

Fiver Over a year ago

ok, I think you should annotate the queryset...I've edited my answer

aroooo Over a year ago

Wow, had no idea this existed. Looking at a few examples and I'm even more confused about how it works, pretty amazed.

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