old_contents: from django.contrib.auth.models import User
  from rest_framework import serializers, viewsets
  from .models import Category, Image, Post
  
  
  class CategorySerializer(serializers.ModelSerializer):
      class Meta:
          model = Category
  
  
  class ImageSerializer(serializers.ModelSerializer):
      class Meta:
          model = Image
  
  
  class UserSerializer(serializers.Serializer):
      username = serializers.CharField(max_length=200)
  
  
  class PostSerializer(serializers.ModelSerializer):
      category = CategorySerializer()
      image = ImageSerializer()
      author = UserSerializer()
  
      class Meta:
          model = Post
  
new_contents: from django.contrib.auth.models import User
  from rest_framework import serializers, viewsets
  from .models import Category, Image, Post
  
  
  class CategorySerializer(serializers.ModelSerializer):
      class Meta:
          model = Category
  
  
  class ImageSerializer(serializers.ModelSerializer):
      class Meta:
          model = Image
  
      url = serializers.CharField()
  
  
  class UserSerializer(serializers.Serializer):
      username = serializers.CharField(max_length=200)
  
  
  class PostSerializer(serializers.ModelSerializer):
      category = CategorySerializer()
      image = ImageSerializer()
      author = UserSerializer()
  
      class Meta:
          model = Post
  
subject: Add serializer