Question

我希望找到一个好的模式来推迟执行操作，直到当前事务成功提交为止。例如，我可能有：

with pool(...)  as connection:
    execute_steps(connection)

其中子函数通过将它们提交到外部消息队列（rabbit / AMQP，...）来启动一个或多个异步任务...仅在事务成功提交时才启动。那是

 def substep(connection): 
       submit_to_queue()

如果事务随后失败（在提交到队列之后），或者在事务提交之前执行了放在队列中的作业，则

...可能会失败。所以 - submit_to_queue必须在connection.com之后执行。

这样做的一个自然方法是收集回调步骤：

def substep(connection):

  def submit_to_queue(): ...
  ...
  connection.on_after_commit(submit_to_queue)
  ...

并且：

@contextmanager
def db_pool(db_name="lb2", current_connection=None):

    connection = connection_pool.getconn()
    connection.on_after_commit = []
    try:

        # Do the work
        yield connection

        connection.commit()

        # Reset the after_success list and execute
        for job in connection.after_success():
            job()
        connection.after_success = [], 

    except Exception:
        connection.rollback()
        connection.after_success = []
        raise

但是，psycopg2的连接是一个不可变对象。那么...是否有另一种方法可以使用psycopg2注册执行后回调？

感谢。

Answer 1

子类化psycopg2.extensions.connection将允许您向对象添加属性（请参阅解释here了解原因）：

In [44]: import psycopg2

In [45]: import psycopg2.extensions

In [46]: conn = psycopg2.connect('dbname=postgres')

In [47]: conn.foo = 'bar'
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-47-3ab9f2c6e77e> in <module>()
----> 1 conn.foo = 'bar'

AttributeError: 'psycopg2.extensions.connection' object has no attribute 'foo'

In [48]: class MyConnection(psycopg2.extensions.connection):
   ...       pass
   ...

In [49]: conn2 = MyConnection('dbname=postgres')

In [50]: conn2.foo = 'bar'

In [51]: conn2.foo
Out[51]: 'bar'

psycopg2 - 在提交之前推迟操作

1 个答案: