[Answer]-Django (django-rest-framework) looking for a best practice to find out wether request.user exists in blog.likes

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1👍

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I can think of a two ways to achieve this.

  1. If you just need a boolean True/False whether the Post is liked by the request.user, you can use .extra.

    1.1. Alter your BlogPost Queryset to something like this:

    class BlogPostQuerySet(models.QuerySet):
    def annotate_is_liked_by_user(self, user):
        return self.extra(
            select = {'is_liked': 'EXISTS( \
                SELECT `id` FROM `blogpostlikes` \
                WHERE `blogpostlikes`.`blogpost_id` = `blogpost`.id \
                AND `blogpostlikes`.`user_id` = %s)' % user.id
            }
        )

class BlogPost
    # other stuffs here
    objects = BlogPostQuerySet.as_manager()

    1.2. Alter get_queryset method inside BlogPostList view

    class BlogPostList(ListAPIView):

    def get_queryset(self):
        user = self.request.user
        return BlogPost.objects.annotate_is_liked_by_user(user)

    1.3. Add the new field to the BlogPostSerializer

    class BlogPostSerializer(serializer.ModelSerializer):
    # ....
    is_liked = serializers.BooleanField(source='is_liked')
    # ...

  2. Get the whole BlogPostLike object.

    2.1.Alter the get_queryset method.

    class BlogPostList(ListAPIView):

    def get_queryset(self):
        user = self.request.user
        return BlogPost.objects.prefetch_related(
            Prefetch(
                'likes', 
                queryset=BlogPostLikes.objects.filter(user=user) \
                    .select_related('user'), 
                to_attr='likes_by_request_user'
            )
        )

    2.2. Alter the serializer. But this can be done in two ways:

    2.2.1. Serializing a list with one item inside:

    class BlogPostSerializer(serializer.ModelSerializer):
    # ...
    likes_by_request_user = BlogPostLikesSerializer(many=True)

    and remove the blogpost = BlogPostSerializer() from BlogPostLikesSerializer. I think this can lead to infinite loop.

    2.2.2 Serialize a single object:

    class BlogPostSerializer(serializer.ModelSerializer):
    # ...
    like_by_request_user = BlogPostLikesSerializer(source='get_last_like', required=False)

    but this way you will have to add a new method inside your BlogPost object to return this single Like object

    class BlogPost(models.Model):
    #...
    def get_last_like(self):
        if hasattr(self, 'likes_by_request_user') and len(self.likes_by_request_user) > 0:
            return self.likes_by_request_user[0]
        return None
👤Todor

0👍

You can use a SerializerMethodField to get your flag dynamically, like this:

class BlogPostSerializer(serializer.ModelSerializer):
    user = SomeUserSerializer()
    likes = BlogPostLikesSerializer()
    has_liked = SerializerMethodField("get_has_liked")
    class Meta:
        model = BlogPostLikes
        fields = ("id", "user", "likes", "content", "image", "has_liked")

    def get_has_liked(self, obj):
        user = self.context.get('request').user
        return len([l.user.id == user.id for l in obj.likes]) > 0

However, you’d need to pass the request when instantiating your serializer, by doing something like this: serializer = BlogPostSerializer(context={'request': request})

👤axelcdv

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