IntegrityError at / doctor / Appointment /

Question

мой код

вот моя модель

я получаю нулевую ошибку ограничения

class Patient(models.Model):
    patient_name=models.CharField(max_length=20,
    null=True,blank=True)
    date_of_birth=models.DateField(null=True)
    email=models.EmailField(null=True,blank=True)
    mobile_number=models.IntegerField(null=True)
    family_members=models.IntegerField(null=True)

    def __str__(self):
        return self.patient_name

    def is_staff(self):
        return self.mobile_number


class Doctor(models.Model):
    doctor_name=models.CharField(max_length=20,null=True,blank=True)
    email_id=models.EmailField(null=True,blank=True)
    doctor_number=models.IntegerField(null=True)
    address=models.CharField(max_length=100,null=True,blank=True)

    def __str__(self):
        return self.doctor_name


class Appointment(models.Model):
    user_name=models.ForeignKey(Patient, on_delete=models.CASCADE, related_name='first')
    mobile_no=models.ForeignKey(Patient, on_delete=models.CASCADE, related_name='second')
    def __str__(self):
        return self.user_name

вот мой набор

class AppointmentViewSet(viewsets.ViewSet):
    def create(self,request):
        user_name=request.data.get('user_name')
        mobile_no=request.data.get('mobile_no')
        new=Appointment()
        new.user_name=user_name
        new.mobile_no=mobile_no
        new.save()
        return Response({'done':True})