Django Signals to update a different model

问题

Say I have two models:

class Product(models.Model):
    product = model.CharField()
    quantity = model.IntegerField()

class sale(models.Model)
    product = models.ManyToManyField(Product)
    number_sold = model. IntegerField()

When a sale is made, I'd like the product quantity to be updated. Are signals the best way of going about this?

I was thinking about having sale admit a post_save signal when an object is created or updated. If updated, I would have to know the old and the new values to adjust the quantity properly. The product table would have to be listening for this signal.

I was also thinking about having the product table send a custom signal after it updates the quantity. If quantity < 0 item is on back order, else "success".

I am new to django and signals, but is this an appropriate use for signals or is their a better way to do this? I have read the docs, and watched a pycon video on signals, and read a few examples. I have yet to see signals used in this way, but I can't think of any other way to accomplish this task.

This is how I ended up accomplishing my goal, I am very interested to know if this is the proper way of doing this. I apologize for the models not matching the code below, I simplified my models to make it easier.

@receiver(pre_save, sender=Customer_Order_Products)
    def update_quantity(sender, **kwargs):
        obj = kwargs['instance']
        updated_product = Inventory.objects.get(title = obj.product_id)
        if not obj.id:
            updated_product.quantity -= obj.quantity
        else:
            updated_product.quantity -= (obj.quantity - Customer_Order_Products.objects.get(id = obj.id).quantity)
        Inventory.save(updated_product)

来源：https://stackoverflow.com/questions/13954499/django-signals-to-update-a-different-model