django - get list of objects by filtering a list of objects

问题

I am creating a user activity streams.

models for activity:

class Activity(models.Model):
    actor = models.ForeignKey(User)
    action = models.CharField(max_length=100)
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    pub_date = models.DateTimeField(auto_now_add=True, auto_now=False)

model for Relationship:

class Person(models.Model):
    user = models.OneToOneField(User)
    relationships = models.ManyToManyField('self', through='Relationship', 
                                           symmetrical=False, 
                                           related_name='related_to')
RELATIONSHIP_FOLLOWING = 1
RELATIONSHIP_BLOCKED = 2
RELATIONSHIP_STATUSES = (
    (RELATIONSHIP_FOLLOWING, 'Following'),
    (RELATIONSHIP_BLOCKED, 'Blocked'),
)

class Relationship(models.Model):
    from_person = models.ForeignKey(Person, related_name='from_people')
    to_person = models.ForeignKey(Person, related_name='to_people')
    status = models.IntegerField(choices=RELATIONSHIP_STATUSES)  

def get_relationships(self, status):
    return self.relationships.filter(
        to_people__status=status, 
        to_people__from_person=self)

def get_following(self):
    return self.get_relationships(RELATIONSHIP_FOLLOWING)

In the views:

def home(request):
    if request.user.is_authenticated():
        user = request.user
        userP = Person.objects.get_or_create(user=user)
        userP = userP[0]
        following = userP.get_following()
        activities = Activity.objects.filter(actor__in=following)
        if request.POST:
            form = StatusForm(request.POST, request.FILES)
            if form.is_valid():
                if form.cleaned_data:
                    status = form.save(commit=False)
                    status.user = user
                    status.save()
                    return HttpResponseRedirect('/')

Scenario

• user is following user2 and user3
• user2 is following user and user3
• user3 is following user and user2

Since I am filtering activities with actor=user and not actor=userP (which is an object of type user.person). How will I get a list of user object from the list get_following() method and not of user.person object.

I can however loop through each of the following like so:

    following = userP.get_following()
    users = []
    for u in following:
        users.append(u.user)
    users.append(user)
    activities = Activity.objects.filter(actor__in=users)

But I am hoping that there will be another better way to do it?

Please guide me. Your help will be very much appreciated. Thank you.

回答1:

Use the queryset's values_list() method:

activities = Activity.objects.filter(actor__in=
                                     following.values_list('user', flat=True))

If you want to add another user to actors list then you have to convert valies_list from queryset to regular python list:

actors = list(following.values_list('user', flat=True)) + [user.id]
activities = Activity.objects.filter(actor__in=actors)

来源：https://stackoverflow.com/questions/28148883/django-get-list-of-objects-by-filtering-a-list-of-objects