如何修复模型的django实例

Question

错误消息 AttributeError：'NoneType‘对象没有属性'add’

我正在尝试创建一个模型的实例。card模型应该是患者模型的一个实例，并且患者模型与用户模型有一个外键关系。就像一个病人在医院里有一张卡片。

我的错误来自于perform_create方法

views.py

class PatientCardListAPIView(ListCreateAPIView):
    serializer_class = PatientsCardSerializer
    queryset = Card.objects.all()
    permission_classes = (permissions.IsAuthenticated, IsOwner,  ) 
    def perform_create(self, serializer):
        serializer.save()
        serializer.instance.owner.add(self.request.user)

models.py

from django.db import models
from authentication.models import User
# Create your models here.

class Patient(models.Model):
    name = models.CharField(max_length=255, null=True)
    country = models.CharField(max_length=255, null=True)
    state = models.CharField(max_length=255, null=True)
    phone = models.CharField(max_length=255, null=True)
    email = models.CharField(max_length=255, null=True)
    owner = models.ForeignKey(to=User, null=True, on_delete=models.CASCADE)
    def __str__(self):
        return self.name
        


class Card(models.Model):    
    name = models.CharField(max_length=255, null=True)
    card_number = models.CharField(max_length=255, null=True)    
    owner = models.OneToOneField(Patient, null=True, blank=True, on_delete=models.CASCADE)
    
    def __str__(self):
        return self.name

Answer 1

这应该是：

def perform_create(self, serializer):
    model_instance = serializer.save(owner=self.request.user)

或

def perform_create(self, serializer):
    model_instance = serializer.save()
    model_instance.owner = self.request.user

编辑的.仔细看看您的模型，就会发现您需要重新定义模型。正如您所定义的，Patient类下的owner字段指示您可以有一个用户可以是多个病人.(查询：patient=Patient.objects.get(owner=self.request.user)可能返回多个实例。)。建议的模式应是：

class Patient(models.Model):
    name = models.CharField(max_length=255, null=True)
    country = models.CharField(max_length=255, null=True)
    state = models.CharField(max_length=255, null=True)
    phone = models.CharField(max_length=255, null=True)
    email = models.CharField(max_length=255, null=True)
    **owner = models.OneToOneField(User, null=True)**
    def __str__(self):
        return self.name

class Card(models.Model):    
    name = models.CharField(max_length=255, null=True)
    card_number = models.CharField(max_length=255, null=True)    
    owner = models.OneToOneField(Patient, null=True, blank=True, on_delete=models.CASCADE)

    def __str__(self):
        return self.name

然后你就可以有自己的观点了：

class PatientCardListAPIView(ListCreateAPIView):
    serializer_class = PatientsCardSerializer
    queryset = Card.objects.all()
    permission_classes = (permissions.IsAuthenticated, IsOwner,  ) 
    
    def perform_create(self, serializer):
        card_instance = serializer.save()
        patient = Patient.objects.get(owner=self.request.user)
        card_instance.owner = patient

Answer 2

我在过去的24小时里几乎因为这个问题而对编程感到气馁，但是这个社区帮助了我，尽管他们没有给出我所需要的答案，他们让我自己发现了答案，我说谢谢stackoverflow社区.

解决了，我终于发现了我做错了什么。卡片不仅是病人的，也是医院的，所以卡片需要与医院和病人的关系。

models.py

 class Patient(models.Model):
        name = models.CharField(max_length=255, null=True)
        country = models.CharField(max_length=255, null=True)
        state = models.CharField(max_length=255, null=True)
        phone = models.CharField(max_length=255, null=True)
        email = models.CharField(max_length=255, null=True)
        owner = models.ForeignKey(to=User, null=True, on_delete=models.CASCADE)
        def __str__(self):
            return self.name      
    
    class Card(models.Model):    
        name = models.CharField(max_length=255, null=True)
        card_number = models.CharField(max_length=255, null=True)    
        owner = models.OneToOneField(Patient, null=True, blank=True, on_delete=models.CASCADE)
        hospital = models.ForeignKey(User, null=True, blank=True, on_delete=models.CASCADE)        
        def __str__(self):
            return self.name

views.py

class PatientCardListAPIView(ListCreateAPIView):
    serializer_class = PatientsCardSerializer
    queryset = Card.objects.all()
    permission_classes = (permissions.IsAuthenticated, IsOwner,  )         
    def perform_create(self, serializer):
        return serializer.save(hospital=self.request.user)
    def get_queryset(self):
        return self.queryset.filter(hospital=self.request.user)

class PatientCardDetailAPIView(RetrieveUpdateDestroyAPIView):
    serializer_class = PatientsCardSerializer
    permission_classes = (permissions.IsAuthenticated, IsOwner,)
    queryset = Card.objects.all()
    lookup_field = "id"
    def get_queryset(self):
        return self.queryset.filter(hospital=self.request.user)