DRF Serializer Error: AttributeError: 'FeedPostSerializer' object has no attribute 'auth_user'

Question

I'm creating a newsfeed in an APP.

A user is logged in and sees the posting of other users. Therefore I need two user models (user + auth_users)

Now I want to add a boolean field that shows if a post is already liked or not.

I already looked at the documentation and other posts here but I can´t find a solution. The auth_user is shown in the response but I can´t included it in the get_already_liked function

class NewsPostSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(read_only=True)
    auth_user = serializers.PrimaryKeyRelatedField(
        read_only=True,
        default=serializers.CurrentUserDefault()
    )
    attachments = AttachmentSerializer(read_only=True, many=True)
    already_liked = serializers.SerializerMethodField()

    def get_already_liked(self, request):
        liking_kwargs = {
            'post_id': request.id,
            'user_id': self.auth_user
        }
        if LikePost.objects.filter(**liking_kwargs).exists():
            return True
        else:
            return False

    class Meta:
        model = Post
        read_only_fields = (
            'id', "user", 'creation_time_stamp', 'auth_user', 'ready_liked',
        )
        fields = (
            'id', 'user', 'creation_time_stamp', 'last_update_time_stamp',
            'description', 'attachments', 'already_liked', 'auth_user',
        )

UPDATE: In another post I found a solution. My code looks now like this and works:

class NewsPostSerializer(serializers.HyperlinkedModelSerializer):
    user = UserSerializer(read_only=True)
    attachments = PostAttachmentSerializer(read_only=True, many=True)
    already_liked = serializers.SerializerMethodField()

    def get_already_liked(self, obj):
        user = self.context['request'].user.id
        liking_kwargs = {
                    'post_id': obj.id,
                    'user_id': user
        }
        if LikePost.objects.filter(**liking_kwargs).exists():
            return True
        else:
            return False

    class Meta:
        model = Post
        read_only_fields = (
            'id', "user", 'creation_time_stamp', 'attachments', 'already_liked',
        )
        fields = (
            'id', 'user', 'creation_time_stamp', 'last_update_time_stamp',
            'description', 'attachments', 'already_liked',
        )

Thanks to Marco and Shakil

score 0 · Answer 1 · answered Sep 10 '19 at 15:45

I would change the approach here a little bit. For the like counter I'd use something like a model in the database that has a foreign key to the picture and another foreign key to the user, with that in place you can use the reverse relations between the models. For instance:

class Post(models.Model):
    ...
    ...

    def number_of_likes(self):
        return len(self.likes.all())  # dont know if sintax is right, but the idea is to get all the instance of likes that is related to this post. (reverse relation)


class Like(models.Model):

    post = models.ForeignKey(Post, on_delete=models.CASCADE ,related_name='likes')
    user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='all_likes')

So, what I recommend is to insert the counter of likes inside the model of the user, and then you can start playing around with this in the serializers.

Hi Marco, first of all thanks for your answer! I already have a model for the liking. `class LikePost(models.Model): user = models.ForeignKey(User, related_name='like_post_user', on_delete=CASCADE, null=True) post = models.ForeignKey(Post, related_name='like_post', on_delete=CASCADE, null=True) time_stamp = models.DateTimeField(auto_now=True)` My probelm is currently to get the ID of the user that is looged in and wants to receive the feed — Andreas Reichienger, Sep 11 '19 at 05:43

score 0 · Answer 2 · answered Sep 10 '19 at 16:57

0

Your serializerMethodField's arguments are wrong. This should be like this

def get_already_liked(self, obj):
        request = self.context.get('request')
        liking_kwargs = {
            'post_id': request.id, // I have a doubt, is this request.data['id'] 
            'user_id': obj.auth_user
        }
        if LikePost.objects.filter(**liking_kwargs).exists():
            return True
        else:
            return False

answered Sep 10 '19 at 16:57

Shakil

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Hi, thanks for your support on this! I tried your solution, but following problems appeared: 'Post' object has no attribute 'auth_user' and request doesn´t include any values My biggest problem is to get the auth_user. When I hard code all IDs everything works well – Andreas Reichienger Sep 11 '19 at 05:51
`Post` object has no attribute `auth_user` because you mention it is a `read_only_fields` in meta class. request.data should contains those, i have commented this. If you post data then . request.data.get('auth_user') should contain auth_user. – Shakil Sep 11 '19 at 06:01
Hi Shaki, thanks for your quick response. I tried what you suggested. ' request.data.get('auth_user') ' gives me None and not the user id – Andreas Reichienger Sep 11 '19 at 06:14
first remove `auth_user` from `read_only_fields`. Can you please update your question with post data ( possible screen shoot of postman ) and your updated code. This will help us to point out the fault. – Shakil Sep 11 '19 at 06:53
Hi Shakil. I found a solution. Please look at the updated Posting. Thanks for your support! – Andreas Reichienger Sep 11 '19 at 08:18

DRF Serializer Error: AttributeError: 'FeedPostSerializer' object has no attribute 'auth_user'

2 Answers2