Python Django REST框架：反序列化外键失败（多对多）

我有以下型号：

models.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")

serializers.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__'

views.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

我将通过HTTP POST发送以下JSON：

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

但并非如日志中所示，事件id和序列号id未反序列化：

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。我应该如何构造适当的序列化程序使其工作

另外，当我尝试发送JSON时，如下图所示，它失败了：

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

---

发生这种情况是因为您正在创建

EventSerializer

和

HostSerializer

， 将传递的值序列化为

只读

，这意味着它们仅在执行

检索

操作时有效，而不是执行

创建

解决此问题的方法是从

EventHostSerializer

例如：

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

    class Meta:
        model = EventHost
        fields = '__all__'

---

我已经从EventSerializer和HostSerializer中删除了read_only=True参数，并打开了debug以查看有什么问题，现在我的HTTP POST请求做了什么，它试图创建新主机和新事件。这不是我需要的。我只需要引用event和host就可以在eventhost表中创建新条目

只是做个记录。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

---

由于

event

和

serialnr

是

EventHost

上的外键，您需要发送已经存在的数据，因此我建议使用

PrimaryKeyRelatedField

这样，如果您发送的id在数据库中不存在，您将得到验证

您需要发送如下数据：

{事件：4，序列号：1234，其他文件：20}

并将序列化程序更改为：

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

稍后编辑：

我发现有一个名为django extra fields的库以更好的方式实现了这一点

---

我已经试过了，但是我得到了：错误的请求：/api/v1/eventhosts/[06/Feb/2020 09:45:17]“POST/api/v1/eventhosts/HTTP/1.1”400166。有没有办法追踪我的请求出了什么问题？我用HTTP POST嵌套或扁平发送的JSON格式应该是什么？

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__'