How to get all related objects in relationship model with single queryset?

Question

I want to get all objects from a User model with single queryset, but I have no idea on how to do it.

I got a 2 relationship model to user model, I can get the objects with these code below

User.objects.get(id=1).profile
User.objects.get(id=1).groups

But how can i get all objects of user with single queryset only?

Answer 1

Use select_related and prefetch_related, as described here:

user = User.objects.select_related('profile').prefetch_related('groups').get(id=1)
user.profile  # does not query the database again
user.groups  # does not query the database again

Note however that since user <-> groups is a m2m relationship, this will hit the database twice in any case. If you're only fetching one specific user, adding the prefetch_related doesn't really make a difference. It does make a difference if you loop through a list of users, since only one query is required to fetch all m2m related groups, instead of one query for each user:

users = User.objects.select_related('profile').prefetch_related('groups')\
     .filter(is_staff=True)
for user in users:  # 2 queries
    print(user.profile)
    for group in user.groups:  # no database query
        print(group.name)