How do I pull in data from multiple models into a specific model serializer?-CodePudding

I have this model that represents a bookmark or favorite. It has multiple foreign keys to other models. In the api I would like to pull in the data from each of the models that is referenced in the particular bookmark.

The model:

class Bookmark(models.Model):
    marktype = models.CharField(max_length=10)
    post = models.OneToOneField(Post, on_delete=models.CASCADE, null=True, blank=True)
    question = models.OneToOneField(Question, on_delete=models.CASCADE, null=True, blank=True)
    owner = models.ForeignKey(User, on_delete=models.CASCADE)
    
    created_at = models.DateTimeField(auto_now_add=True, verbose_name="created at")
    updated_at = models.DateTimeField(auto_now=True, verbose_name="updated at")

    class Meta:
        verbose_name = "bookmark"
        verbose_name_plural = "bookmarks"
        ordering = ["created_at"]
        db_table = "bookmarks"

    def __str__(self):
        return "{}'s bookmark".format(self.owner.username)

I tried to use a SerializerMethodField but I get an error: 'NoneType' object has no attribute 'id'

Here is the serializer

class BookmarkSerializer(serializers.ModelSerializer):
    post = serializers.SerializerMethodField()
    question = serializers.SerializerMethodField()

    class Meta:
        model = Bookmark
        fields = '__all__'

    def get_post(self, obj):
        obj = Post.objects.get(id=obj.post.id)
        post = ShortPostSerializer(obj)
        return post.data

    def get_question(self, obj):
        obj = Question.objects.get(id=obj.question.id)
        question = ShortQuestionSerializer(obj)
        return question.data

what am I doing wrong please?

CodePudding user response：

You can update your serializer like the following (You can short it as you want or use your ShortQuestionSerializer as well instead of QuestionSerializer),

class QuestionSerializer(serializers.ModelSerializer):

    class Meta:
        model = Question
        fields = '__all__'

class PostSerializer(serializers.ModelSerializer):

    class Meta:
        model = Post
        fields = '__all__'

class BookmarkSerializer(serializers.ModelSerializer):
    post = PostSerializer()
    question = QuestionSerializer()

    class Meta:
        model = Bookmark
        fields = '__all__'