Django post_save() 信号实现 [英] Django post_save() signal implementation

问题描述

我有一个关于 django 的问题.

I have a question about django.

我这里有多对多模型

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.如何实现触发器?我想要的是每当创建交易明细时，我希望产品的库存金额减去交易明细中的金额.

For 1 cart object created, I can insert as many as new TransactionDetail object (the product and amount). My question is. How can I implement the trigger? What I want is whenever a Transaction detail is created, I want the amount of the product's stock is substracted by the amount in the transactiondetail.

我已经阅读了 post_save() 但我不确定如何实现它.也许是这样的

I've read about post_save() but I'm not sure how to implement it. maybe something like this

什么时候:

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

推荐答案

如果你真的想使用信号来实现这一点，这里是简要的方法，

If you really want to use signals to achieve this, here's briefly how,

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()

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