如何在无attrs参数的方法中访问DRF序列化器的字段属性

你报错的核心原因是：self.participants 指向的是序列化器定义的字段对象，既不是Conversation模型实例的关联属性，也不是序列化后的participants数据列表。SerializerMethodField对应的方法会自动传入当前正在序列化的模型实例obj，你只需要把这个参数透传给get_other_user即可。

修改后的完整代码 #

class ConversationSerializer(serializers.ModelSerializer): 
    other_username = serializers.SerializerMethodField(method_name='get_other_username', read_only=True)
    other_user_email = serializers.SerializerMethodField(method_name='get_other_user_email', read_only=True)
    participants = UsersSerializer(many=True, read_only=True)

    class Meta:
        model = Conversation
        fields = ['conversation_id' ,'participants','other_username', 'other_user_email']

    def get_current_user_id(self):
        return self.context['current_user'].id

    def get_other_user(self, obj):
        # 缓存结果，避免多次调用重复遍历
        if hasattr(self, '_cached_other_user'):
            return self._cached_other_user
        current_user_id = self.get_current_user_id()
        # 直接从Conversation模型实例读取participants关联数据
        for participant in obj.participants.all():
            if participant.id != current_user_id:
                self._cached_other_user = participant
                return participant

    def get_other_username(self, obj):
        other_user = self.get_other_user(obj)
        return other_user.username

    def get_other_user_email(self, obj):
        other_user = self.get_other_user(obj)
        return other_user.email        

如果你需要读取序列化后的participants字典数据，可使用以下版本的get_other_user方法： #

def get_other_user(self, obj):
    if hasattr(self, '_cached_other_user'):
        return self._cached_other_user
    current_user_id = self.get_current_user_id()
    # 主动调用participants字段的序列化方法得到字典列表
    serialized_participants = self.fields['participants'].to_representation(obj.participants.all())
    for participant in serialized_participants:
        if participant['id'] != current_user_id:
            self._cached_other_user = participant
            return participant

对应修改属性读取方式为字典取值即可：

def get_other_username(self, obj):
    other_user = self.get_other_user(obj)
    return other_user['username']

def get_other_user_email(self, obj):
    other_user = self.get_other_user(obj)
    return other_user['email']

内容的提问来源于stack exchange，提问作者Arkash Vijayakumar