old_contents: from django.contrib.auth.models import User
  from .models import ContentItem, Profile, Comment, Hashtag, ContentHashTag, Like
  from rest_framework import serializers
  from rest_framework.validators import UniqueValidator
  
  
  class UserSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = User
          fields = ('id', 'url', 'username', 'password', 'email', 'last_name', 'first_name')
  
      email = serializers.EmailField(validators=[UniqueValidator(queryset=User.objects.all())])
  
      def create(self, validated_data):
          user = User.objects.create_user(**validated_data)
          return user
  
  
  class ProfileSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Profile
          fields = ('id', 'url', 'user', 'personal_info', 'job_title', 'department', 'location', 'expertise',
                    'phone_number', 'contact_skype', 'contact_facebook', 'contact_linkedin', 'user_photo')
  
  
  class ContentItemSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = ContentItem
          fields = ('id', 'url', 'upload_date', 'title', 'description', 'image', 'uploaded_by')
          extra_kwargs = {'image': {'required': 'True'}}
  
      def create(self, validated_data):
          return ContentItem.objects.create(**validated_data)
  
  
  class HashtagSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Hashtag
          fields = ('id', 'url', 'hashtag_text')
  
  
  class ContentHashtagSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = ContentHashTag
          fields = ('id', 'url', 'content_id', 'hashtag_id')
  
  
  class LikeSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Like
          fields = ('id', 'url', 'user_id', 'content_id')
       
      validators = [
          UniqueTogetherValidator(
              queryset=Like.objects.all(),
              fields=('user_id', 'content_id')
          )
      ]
  
  
  class CommentSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Comment
          fields = ('id', 'url', 'comment_text', 'publication_date', 'author', 'contentItem')
  
new_contents: from django.contrib.auth.models import User
  from .models import ContentItem, Profile, Comment, Hashtag, ContentHashTag, Like
  from rest_framework import serializers
  from rest_framework.validators import UniqueValidator, UniqueTogetherValidator
  
  
  class UserSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = User
          fields = ('id', 'url', 'username', 'password', 'email', 'last_name', 'first_name')
  
      email = serializers.EmailField(validators=[UniqueValidator(queryset=User.objects.all())])
  
      def create(self, validated_data):
          user = User.objects.create_user(**validated_data)
          return user
  
  
  class ProfileSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Profile
          fields = ('id', 'url', 'user', 'personal_info', 'job_title', 'department', 'location', 'expertise',
                    'phone_number', 'contact_skype', 'contact_facebook', 'contact_linkedin', 'user_photo')
  
  
  class ContentItemSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = ContentItem
          fields = ('id', 'url', 'upload_date', 'title', 'description', 'image', 'uploaded_by')
          extra_kwargs = {'image': {'required': 'True'}}
  
      def create(self, validated_data):
          return ContentItem.objects.create(**validated_data)
  
  
  class HashtagSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Hashtag
          fields = ('id', 'url', 'hashtag_text')
  
  
  class ContentHashtagSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = ContentHashTag
          fields = ('id', 'url', 'content_id', 'hashtag_id')
  
  
  class LikeSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Like
          fields = ('id', 'url', 'user_id', 'content_id')
       
      validators = [
          UniqueTogetherValidator(
              queryset=Like.objects.all(),
              fields=('user_id', 'content_id')
          )
      ]
  
  
  class CommentSerializer(serializers.HyperlinkedModelSerializer):
      class Meta:
          model = Comment
          fields = ('id', 'url', 'comment_text', 'publication_date', 'author', 'contentItem')
  
subject: Add validator import