在Django REST框架中，我如何告诉序列化器更新成员字段，而不是尝试从头开始创建它？

from rest_framework import serializers

class MySerializer(serializers.Serializer):
    # 定义需要序列化/反序列化的字段
    id = serializers.IntegerField(read_only=True)
    name = serializers.CharField()
    email = serializers.EmailField()

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

from rest_framework.views import APIView
from rest_framework.response import Response

class MyView(APIView):
    def put(self, request, pk):
        instance = MyModel.objects.get(pk=pk)
        serializer = MySerializer(instance, data=request.data, partial=True)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)