Django post_save：数据库尚未更新？

Question

I'm writing a Django application for ordering stuff. All orders have a certain type Type. If Type.is_common == true, it needs to be included in a delivery no matter if a user orders this type or not. I'm using a post_save signal to check if my db already has a common order for a user for a certain delivery. Here is the code:

@receiver(post_save, sender=Order)
def create_common_order(sender, instance=None, created=False, **kwargs):
    """ This signal handler creates common orders (if delivery type
    definition contains any common types) for every first order of a
    user for a certain delivery. """
    # Don't handle this if the order is not for a delivery
    if not created or not instance or not instance.delivery:
        return

    # Don't handle Order with common types
    if instance.type.is_common:
        return

    # Loop through all types in type definition of delivery
    for t in Type.objects.all():
        # Look for a 'is_common' type
        if type.is_common:
            # Get or create an order with the respective values
            Order.objects.get_or_create(
               delivery=instance.delivery, 
               user=instance.user,
               type=type,
               defaults={'count':1}
               )

My problem is the following: From time to time it happens that two common orders are created (if two new orders are created at almost the same time). But why? Is the db not yet updated in post_save? How can I prevent this behavior? I'm using a sqlite3 db.

Answer 1

好的，所以在尝试了许多不同的事情之后，我终于找到了一个解决方案（实际上很简单）：只需在调用get_or_create（）之前添加Order.objects.update（）即可。