Django REST 框架：反序列化外键失败（多对多）

Question

我有以下模型：

模型.py：

class Host(models.Model):
    serialnr = models.IntegerField(primary_key=True)
    ...some other fields...

class Event(models.Model):
    id = models.AutoField(primary_key=True)
    hosts = models.ManyToManyField(Host, through='EventHost')
    ...some other fields...

class EventHost(models.Model):
    serialnr = models.ForeignKey(Host, on_delete=models.PROTECT)
    event = models.ForeignKey(Event, on_delete=models.CASCADE)
    ...some other fields...
    class Meta:
        unique_together = ("serialnr", "event")

序列化程序.py：

class EventSerializer(serializers.ModelSerializer):
    class Meta:
        model = Event
        fields = '__all__'

class HostSerializer(serializers.ModelSerializer):
    class Meta:
        model = Host
        fields = '__all__'

class EventHostSerializer(serializers.ModelSerializer):
    event =  EventSerializer(read_only=True)
    serialnr = HostSerializer(read_only=True)

    class Meta:
        model = EventHost
        fields = '__all__'

视图.py

class EventViewSet(viewsets.ModelViewSet):
    queryset = Event.objects.order_by('-date')
    serializer_class = EventSerializer

class HostViewSet(viewsets.ModelViewSet):
    queryset = Host.objects.order_by('-serialnr')
    serializer_class = HostSerializer

class EventHostViewSet(viewsets.ModelViewSet):
    queryset = EventHost.objects.order_by('-start_date')
    serializer_class = EventHostSerializer

我使用 HTTP POST 发送以下 JSON：

{event: {id: 4}, serialnr: {serialnr: 1234}, other_filed: 20} 

但它不是 event_id 和 serialnr_id 没有反序列化，如日志中所示：

psycopg2.errors.NotNullViolation: null value in column "event_id" violates not-null constraint
DETAIL:  Failing row contains (12, 20, null, null).

我可以用 HTTP GET 读取数据，但不能用 POST 写入。 我应该如何构建适当的序列化程序以使其工作？

此外，当我尝试像下面这样发送 JSON 时，它失败了：

{event_id: 4, serialnr_id: 1234, other_filed: 20} 

Answer 1

由于event和serialnr上ForeignKeys EventHost你需要发送的数据已经存在，所以我建议使用PrimaryKeyRelatedField这样你会得到验证，如果你发送不存在于你的数据库的ID。

您需要像这样发送数据： {event: 4, serialnr: 1234, other_filed: 20}

并将您的序列化程序更改为：

from rest_framework.relations import PrimaryKeyRelatedField


class EventHostSerializer(serializers.ModelSerializer):
    event = PrimaryKeyRelatedField(queryset=Event.objects.all())
    serialnr = PrimaryKeyRelatedField(queryset=Host.objects.all())

    class Meta:
        model = EventHost
        fields = '__all__'

    # add this(if needed) to get event/serialnr representation instead of primary keys 
    # might be usefull for you when you retrieve the object back (in list/retrieve operations)
    def to_representation(self, instance):
        ret = super().to_representation(instance)
        ret['event'] = EventSerializer(context=self.context).to_representation(instance.event)
        ret['serialnr'] = HostSerializer(context=self.context).to_representation(instance.serialnr)
        return ret

后期编辑：

我发现有一个名为 django-extra-fields 的库，它以更好的方式做到这一点。

https://github.com/Hipo/drf-extra-fields#presentableprimarykeyrelatedfield

from drf_extra_fields.relations import PresentablePrimaryKeyRelatedField


class EventHostSerializer(serializers.ModelSerializer):
    event = PresentablePrimaryKeyRelatedField(
        queryset=Event.objects.all(), presentation_serializer=EventSerializer
    )
    serialnr = PresentablePrimaryKeyRelatedField(
        queryset=Host.objects.all(), presentation_serializer=HostSerializer
    )

    class Meta:
        model = EventHost
        fields = '__all__'

Answer 2

发生这种情况是因为您正在制作EventSerializer和HostSerializer ，将传递的值序列化为read_only这意味着它们只在有retrieve操作时工作，而不是create

解决这个问题的方法是从EventHostSerializer删除read_only EventHostSerializer

像下面这样：

class EventHostSerializer(serializers.ModelSerializer):
    event =  EventSerializer() #read_only=True)
    serialnr = HostSerializer() #read_only=True)

    class Meta:
        model = EventHost
        fields = '__all__'

Answer 3

我已经从EventSerializer和HostSerializer 中删除了read_only=True参数并打开调试以查看有什么问题，现在我的 HTTP POST 请求尝试创建新主机和新事件。 那不是我需要的。 我只需要引用 event 和 host 在 eventhost 表中创建新条目。

只是为了做笔记。 当我使用 django shell 添加新的 eventhost 实例时，它可以工作：

>>> from myapp.models import Host, Event, EventHost
>>> from myapp.serializers import HostSerializer, EventSerializer, EventHostSerializer
myeventhost = EventHost.objects.create(event_id=4, serialnr_id=1234, otherparam=20)
>>> serializedmyeventhost = EventHostSerializer(myeventhost)
>>> serializedmyeventhost.data
{'id': 29, 'event': OrderedDict([('id', 4), ...etc