[英]How to access foreign key value in a django model?
我正在嘗試構建一個簡單的“隊列”應用程序,在該應用程序中,用戶可以在某個房間的隊列中用數字取票。
我在定義Ticket.number和Room.next_number_to_take之間的關系時遇到了一些問題。 創建票證時,Ticket.number的值應為Room.next_number_to_take,但是,如果不為該類指定初始化函數,我不知道如何用“ Django”語言定義它。
這是我失敗的嘗試(失敗了故障單的save方法):
from django.db import models
from django.utils import timezone
from django.contrib.auth.models import User
# Create your models here.
class Room(models.Model):
name = models.CharField(max_length=100)
room_master = models.ForeignKey(User, on_delete=models.CASCADE)
current_visitor_number = models.BigIntegerField(default=0)
next_number_to_take = models.BigIntegerField(default=0)
class Ticket(models.Model):
request_date = models.DateTimeField(default=timezone.now)
user = models.ForeignKey(User, on_delete=models.CASCADE)
room = models.ForeignKey(Room, on_delete=models.CASCADE)
number = models.BigIntegerField(default=0)
def save(self, *args, **kwargs):
self.number = self.room.next_number_to_take
self.room.next_number_to_take += 1
super(Ticket, self).save(*args, **kwargs)
我以前嘗試過以下同樣失敗的方法:
class Ticket(models.Model):
request_date = models.DateTimeField(default=timezone.now)
user = models.ForeignKey(User, on_delete=models.CASCADE)
room = models.ForeignKey(Room, on_delete=models.CASCADE)
number = room.next_number_to_take
room.next_number_to_take += 1
我自己還沒有嘗試過此代碼。 我認為,當您更改“ Room
模型的next_number
,不會保存該模型。 所以我添加了另一行。 看看它是否有效,如果有任何錯誤,請盡快與我聯系。
def save(self, *args, **kwargs):
self.number = self.room.next_number_to_take
self.room.next_number_to_take += 1 # this line is ok but you need to save it
self.room.save() # this is the new line to add
super(Ticket, self).save(*args, **kwargs)
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