myapp/serializers.py

from rest_framework import serializers

class ItemSerializer(serializers.Serializer):
    url = serializers.URLField(max_length=200)

    def create(self, validated_data):
        # Typically, you would save the data to a database here.
        # As you're not using a database for this instance, you can just return the validated data.
        return validated_data

    def update(self, instance, validated_data):
        instance.url = validated_data.get('url', instance.url)
        instance.save()
        return instance