在Django RESTframework中對模型中的字段進行自動計算

Question

所以我有一個模型，該模型的屬性在api收到POST請求時自動計算。 該模型是賬單模型，其中總付款額是根據numberOfHours * paymentRate計算的。 Django不允許我通過設置默認值來這樣做。 有沒有辦法做到這一點？

模型

class Bill(models.Model):
    billID = models.AutoField(primary_key=True)
    bill_dt = models.DateField()
    hours =  models.FloatField()
    workAssignmentID_fk = models.ForeignKey(WorkAssignment, null=True, default=None)
    totalPayment = models.FloatField(default=0)

    def __unicode__(self):
        return u'%s' % (self.bill_dt)

    def __str__(self):
        return u'%s' % (self.bill_dt)

串行

class ReadBillSerializer(serializers.HyperlinkedModelSerializer):
    workAssignmentID_fk = ReadWorkAssignmentSerializer()

    class Meta:
        model = Bill
        fields = ('url', 'bill_dt', 'hours', 'workAssignmentID_fk', 'totalPayment')

class WriteBillSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = Bill
        fields = ('url', 'bill_dt', 'hours', 'workAssignmentID_fk', 'totalPayment')

視圖

class BillViewSet(viewsets.ModelViewSet):
    queryset = Bill.objects.all()

    def get_serializer_class(self, *args, **kwargs):        
        if self.request.method == 'POST' or self.request.method == 'PUT':
            return WriteBillSerializer
        return ReadBillSerializer

在模型Bill中，我希望totalPayment =小時* workAssignmentID_fk.paymentRate。

paymentRate是workAssignmentID_fk中的一個屬性。

Answer 1

您可以在視圖中覆蓋perform_create()函數，並將totalPayment的值totalPayment給序列化器的save()方法。

保存新的對象實例時，將調用perform_create() 。 您可以使用此對象創建掛鈎。

class BillViewSet(viewsets.ModelViewSet):
    queryset = Bill.objects.all()

    def get_serializer_class(self, *args, **kwargs):        
        if self.request.method == 'POST' or self.request.method == 'PUT':
            return WriteBillSerializer
        return ReadBillSerializer

    def perform_create(self, serializer):
        hours = serializer.validated_data['hours'] # get the value of hours
        work_assignment_object = <get_the_workAssignmentID_fk_object_from_passed_url>
        payment_rate = work_assignment_object.paymentRate # get the value of 'paymentRate' from work assignment object
        total_payment = hours*payment_rate # calculate value of total payment
        serializer.save(total_payment=total_payment, workAssignmentID_fk=work_assignment_object) # pass the value of total payment to be saved and the work assignment object