python - Django REST框架: deserializing foreign key fails (many-to-many)

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")

序列化器.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__'

View .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).

我可以使用 HTTP GET 读取数据，但无法使用 POST 写入数据。我应该如何构建正确的序列化器才能使其工作？

此外，当我尝试发送如下 JSON 时，它失败了:

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

Answer 1

由于 event 和 serialinr 是 EventHost 上的外键，因此您需要发送已存在的数据，因此我建议使用 PrimaryKeyRelatedField 通过这种方式，如果您发送数据库中不存在的 ID，您就会得到验证。

您需要发送如下数据:{事件:4，serialnr:1234，other_filed:20}

并将序列化器更改为:

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 的库可以更好地完成此操作。

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__'