6

考虑这个简单的例子：

# a bank account class
class Account:
    @transaction.commit_on_success
    def withdraw(self, amount):
        # code to withdraw money from the account 

    @transaction.commit_on_success
    def add(self, amount):
        # code to add money to the account

# somewhere else
@transaction.commit_on_success
def makeMoneyTransaction(src_account, dst_account, amount):
    src_account.withdraw(amount)
    dst_account.add(amount)

（取自https://code.djangoproject.com/ticket/2227）

如果在 中引发异常，则仍将提交inAccount.add()的事务并且会丢失金钱，因为 Django 当前不处理嵌套事务。Account.withdraw()

如果不对 Django 应用补丁，我们如何确保提交被发送到数据库，但前提是@transaction.commit_on_success装饰器下的 main 函数完成而不会引发异常？

我遇到了这个片段：http ://djangosnippets.org/snippets/1343/ ，它似乎可以完成这项工作。如果我使用它，我应该注意什么缺点？

如果您能提供帮助，请提前非常感谢。

PS为了可见性，我正在复制之前引用的代码片段：

def nested_commit_on_success(func):
    """Like commit_on_success, but doesn't commit existing transactions.

    This decorator is used to run a function within the scope of a 
    database transaction, committing the transaction on success and
    rolling it back if an exception occurs.

    Unlike the standard transaction.commit_on_success decorator, this
    version first checks whether a transaction is already active.  If so
    then it doesn't perform any commits or rollbacks, leaving that up to
    whoever is managing the active transaction.
    """
    commit_on_success = transaction.commit_on_success(func)
    def _nested_commit_on_success(*args, **kwds):
        if transaction.is_managed():
            return func(*args,**kwds)
        else:
            return commit_on_success(*args,**kwds)
    return transaction.wraps(func)(_nested_commit_on_success)
4

2 回答 2

5

这个片段的问题是它不能让你在不回滚外部事务的情况下回滚内部事务。例如：

@nested_commit_on_success
def inner():
    # [do stuff in the DB]

@nested_commit_on_success
def outer():
    # [do stuff in the DB]
    try:
        inner()
    except:
        # this did not work, but we want to handle the error and
        # do something else instead:

        # [do stuff in the DB]

outer()

在上面的示例中，即使inner()引发异常，其内容也不会回滚。

您需要的是内部“事务”的保存点。对于您的代码，它可能如下所示：

# a bank account class
class Account:
    def withdraw(self, amount):
        sid = transaction.savepoint()
        try:
            # code to withdraw money from the account
        except:
            transaction.savepoint_rollback(sid)
            raise

    def add(self, amount):
        sid = transaction.savepoint()
        try:
            # code to add money to the account
        except:
            transaction.savepoint_rollback(sid)
            raise

# somewhere else
@transaction.commit_on_success
def makeMoneyTransaction(src_account, dst_account, amount):
    src_account.withdraw(amount)
    dst_account.add(amount)

从 Django 1.6 开始，atomic()装饰器就是这样做的：它使用事务来外部使用装饰器，而任何内部使用都使用保存点。

于 2013-02-12T21:18:46.567 回答
2

Django 1.6 引入了@atomic，这正是我想要的！

它不仅支持“嵌套”事务，而且还替换了旧的、功能较弱的装饰器。跨不同 Django 应用程序的事务管理具有独特且一致的行为是很好的。

于 2013-09-04T18:15:28.503 回答