无法使用Django Rest框架创建嵌套注释功能

Question

我正在尝试使用django rest框架进行嵌套注释功能。 我正在使用Django 2.2和其他框架版本3.10.2，但是在这里，我正在使用Django 1.9的youtube中观看视频。 无论我在URL中传递了什么值，它总是返回验证错误，指出 model_qs为空。 我无法解决此问题。有人可以调查一下吗 让我指出我在这里做错了。

from django.contrib.auth.models import User
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType

urls.py

urlpatterns = [
    path('create/', CommentCreateAPIView.as_view(), name='create'),
]

model.py

class CommentManager(models.Manager):
    def all(self):
        qs = super(CommentManager, self).filter(parent=None)
        return qs

    def filter_by_instance(self, instance):
        content_type = ContentType.objects.get_for_model(instance.__class__)
        obj_id = instance.id
        qs = super(CommentManager, self).filter(content_type=content_type, object_id=obj_id).filter(parent=None)
        return qs

    def create_by_model_type(self, model_type, slug, content, user, parent_obj=None):
        model_qs = ContentType.objects.filter(model=model_type)
        if model_qs.exists():
            some_model = model_qs.first().model_class()
            obj_qs = some_model.objects.filter(slug=slug)
            if obj_qs.exists() and obj_qs.count() == 1:
                instance = self.model()
                instance.content = content
                instance.user = user
                instance.content_type = model_qs.first()
                instance.object_id = obj_qs.first().id
                if parent_obj:
                    instance.parent = parent_obj
                instance.save()
                return instance
        return None


class Comment(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, default=1)
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    content_object = GenericForeignKey('content_type', 'object_id')
    parent = models.ForeignKey('self', null=True, blank=True, on_delete=models.CASCADE)
    content = models.TextField()
    timestamp = models.DateTimeField(auto_now_add=True)

    objects = CommentManager()

    class Meta:
        ordering = ['-timestamp']

    def __unicode__(self):
        return str(self.user.username)

    def __str__(self):
        return str(self.user.username)

    def get_absolute_url(self):
        return reverse("comments:thread", kwargs={"id": self.id})

    def get_delete_url(self):
        return reverse("comments:delete", kwargs={"id": self.id})

    def children(self):  # Replies
        return Comment.objects.filter(parent=self)

    @property
    def is_parent(self):
        if self.parent is not None:
            return False
        return True

serializers.py

def create_comment_serializer(model_type='post', slug=None, parent_id=None, user=None):
    class CommentCreateSerializer(ModelSerializer):
        class Meta:
            model = Comment
            fields = [
                'id',
                'parent',
                'content',
                'timestamp',
            ]

        def __init__(self, *args, **kwargs):
            self.model_type = model_type
            self.slug = slug
            self.parent_obj = None
            if parent_id:
                parent_qs = Comment.objects.filter(id=parent_id)
                if parent_qs.exists() and parent_qs.count() == 1:
                    self.parent_obj = parent_qs.first()
            return super(CommentCreateSerializer, self).__init__(*args, **kwargs)

        def validate(self, data):
            model_type = self.model_type
            model_qs = ContentType.objects.filter(model=model_type)

            print(model_qs)  # This always return <QuerySet []>

            if not model_qs.exists() or model_qs.count() != 1:
                raise ValidationError("This is not a valid content types")
            some_model = model_qs.first().model_class()
            obj_qs = some_model.objects.filter(slug=self.slug)
            if not obj_qs.exists() or obj_qs.count() != 1:
                raise ValidationError("This is not a valid slug")
            return data

        def create(self, validated_data):
            content = validated_data.get("content")
            if user:
                main_user = user
            else:
                main_user = User.objects.all().first()
            model_type = self.model_type
            slug = self.slug
            parent_obj = self.parent_obj
            comment = Comment.objects.create_by_model_type(model_type, slug, content, main_user, parent_obj=parent_obj,)
            return comment

    return CommentCreateSerializer

views.py

class CommentCreateAPIView(CreateAPIView):
    queryset = Comment.objects.all()
    # permission_classes = [IsAuthenticated]

    def get_serializer_class(self):
        model_type = self.request.GET.get("type")
        slug = self.request.GET.get("slug")
        parent_id = self.request.GET.get("parent_id", None)
        return create_comment_serializer(
            model_type=model_type,
            slug=slug,
            parent_id=parent_id,
            user=self.request.user
        )