Django post_save()信号实现

Question

我有一个关于django的问题.

我在这里有ManyToMany模型

class Product(models.Model):
     name = models.CharField(max_length=255)
     price = models.DecimalField(default=0.0, max_digits=9, decimal_places=2)
     stock = models.IntegerField(default=0)

     def  __unicode__(self):
         return self.name

class Cart(models.Model):
    customer = models.ForeignKey(Customer)
    products = models.ManyToManyField(Product, through='TransactionDetail')
    t_date = models.DateField(default=datetime.now())
    t_sum = models.FloatField(default=0.0)

    def __unicode__(self):
         return str(self.id)

class TransactionDetail(models.Model):
    product = models.ForeignKey(Product)
    cart = models.ForeignKey(Cart)
    amount = models.IntegerField(default=0)

对于创建的1个购物车对象,我可以插入尽可能多的新TransactionDetail对象(产品和金额).我的问题是.我该如何实现触发器？我想要的是每当创建交易细节时,我希望产品库存的数量减去transactiondetail中的金额.

我读过有关post_save()但我不确定如何实现它.也许这样的事情

when:post_save(TransactionDetail,Cart)#Cart对象,其中TransactionDetail.cart = Cart.id

post_save(TransactionDetail, 
       Cart) #Cart object where TransactionDetail.cart= Cart.id
Cart.stock -= TransactionDetail.amount

Answer 1

如果你真的想用信号来达到这个目的,这里简要介绍一下,

from django.db.models.signals import post_save
from django.dispatch import receiver

class TransactionDetail(models.Model):
    product = models.ForeignKey(Product)

# method for updating
@receiver(post_save, sender=TransactionDetail, dispatch_uid="update_stock_count")
def update_stock(sender, instance, **kwargs):
    instance.product.stock -= instance.amount
    instance.product.save()

Answer 2

我个人会覆盖TransactionDetail的save()方法,并在那里保存新的TransactionDetail然后运行

self.product.stock -= self.amount
self.product.save()

Answer 3

如果你想避免获取maximum recursion depth exceeded,那么你应该在信号处理程序中保存之前断开信号.上面的例子(Kenny Shen的回答)将是:

from django.db.models.signals import post_save
from django.dispatch import receiver

class TransactionDetail(models.Model):
    # ... fields here

# method for updating
@receiver(post_save, sender=TransactionDetail, dispatch_uid="update_stock_count")
def update_stock(sender, instance, **kwargs):
 instance.product.stock -= instance.amount

 post_save.disconnect(update_stock, sender=TransactionDetail)
 instance.product.save()
 post_save.connect(update_stock, sender=TransactionDetail)

这在模型的断开信号和django中的重新连接中有详细描述,并有一个更抽象和有用的例子.

另请参阅:django文档中的https://docs.djangoproject.com/en/2.0/topics/signals/#disconnecting-signals.

Answer 4

如果你真的想在 django 中使用信号，请尝试以下操作：

#import inbuilt user model
from django.contrib.auth.models import User
from django.db.models.signals import post_save
from django.dispatch import receiver

@receiver(post_save, sender=User)
def create_profile(sender, **kwargs):
    # write you functionality
    pass
   

然后default_app_config在init文件中添加

 default_app_config = "give your AppConfig path"