Django Rest Framework：具有通用外键的可写嵌套序列化器

Question

有示例如何创建像这样的可写嵌套序列化程序，然后如何序列化通用外键（此处）。

但是我找不到同时进行这两项操作的方法，即如何为通用外键字段创建嵌套的可写序列化程序。

在我的模型中，有一个Meeting模型，GenericForeignKey其可以是DailyMeeting或可以是WeeklyMeeting：

class Meeting(models.Model):
    # More fields above
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.PositiveIntegerField()
    recurring_meeting = GenericForeignKey('content_type', 'object_id')

class DailyMeeting(models.Model):
    meeting = GenericRelation(Meeting)
    # more fields

class WeeklyMeeting(models.Model):
    meeting = GenericRelation(Meeting)
    # more fields

然后，在我的中创建了一个自定义字段serializers.py：

class RecurringMeetingRelatedField(serializers.RelatedField):
    def to_representation(self, value):
        if isinstance(value, DailyMeeting):
            serializer = DailyMeetingSerializer(value)
        elif isinstance(value, WeeklyMeeting):
            serializer = WeeklyMeetingSerializer(value)
        else:
            raise Exception('Unexpected type of tagged object')
        return serializer.data


class MeetingSerializer(serializers.ModelSerializer):
    recurring_meeting = RecurringMeetingRelatedField()

    class Meta:
        model = Meeting
        fields = '__all__'

我正在传递一个类似于以下内容的JSON：

{
    "start_time": "2017-11-27T18:50:00",
    "end_time": "2017-11-27T21:30:00",
    "subject": "Test now",
    "moderators": [41],
    "recurring_meeting":{
        "interval":"daily",
        "repetitions": 10,
        "weekdays_only": "True"
        }
}

但是问题是我遇到以下错误：

AssertionError：关系字段必须提供queryset参数，覆盖get_queryset或设置read_only = True。

为什么关系领域必须是read_only？如果我将其设置为read_only，则不会data在序列化器中传递它。

我必须提供哪种类型的查询集？

Answer 1

您还需要实现to_internal_value，并且可以只使用普通Field类。

from rest_framework.fields import Field

class RecurringMeetingRelatedField(Field):
    def to_representation(self, value):
        if isinstance(value, DailyMeeting):
            serializer = DailyMeetingSerializer(value)
        elif isinstance(value, WeeklyMeeting):
            serializer = WeeklyMeetingSerializer(value)
        else:
            raise Exception('Unexpected type of tagged object')
        return serializer.data

    def to_internal_value(self, data):
        # you need to pass some identity to figure out which serializer to use
        # supose you'll add 'meeting_type' key to your json
        meeting_type = data.pop('meeting_type')

        if meeting_type == 'daily':
            serializer = DailyMeetingSerializer(data)
        elif meeting_type == 'weekly':
            serializer = WeeklyMeetingSerializer(data)
        else:
            raise serializers.ValidationError('no meeting_type provided')

        if serializer.is_valid():
            obj = serializer.save()
        else:
            raise serializers.ValidationError(serializer.errors)

        return obj

如果验证顺利，那么您将在MeetingSerializer验证数据中创建对象，RecurringMeetingRelatedField否则将引发异常。