如何指定在Django中序列化视图中的数据时为外部字段返回的值

from rest_framework import serializers

class MyModelSerializer(serializers.ModelSerializer):
    external_field = serializers.SerializerMethodField()

    def get_external_field(self, obj):
        # 编写获取外部字段值的逻辑
        return "外部字段的值"

    class Meta:
        model = MyModel
        fields = ('field1', 'field2', 'external_field')

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

class MyView(APIView):
    def get(self, request):
        queryset = MyModel.objects.all()
        serializer = MyModelSerializer(queryset, many=True)
        return Response(serializer.data)