from rest_framework import serializers class UsernameSerializer(serializers.Serializer): id = serializers.IntegerField() username = serializers.CharField() real_name = serializers.SerializerMethodField() def __init__(self, *args, **kwargs): self.need_real_name = kwargs.pop("need_real_name", False) super().__init__(*args, **kwargs) def get_real_name(self, obj): return obj.userprofile.real_name if self.need_real_name else None