如何管理这种模式这sqlalchemy

Question

伙计

我发现自己在sqlalchemy重复了很多，我想知道什么是最好的方式来处理它？

try: 
    #do some database query 
    db_session.commit() 
except: #some exception handling 
    db_session.rollback() 

Answer 1

这是从我的工作代码，一个会话注册表包装的方法是正确的。

它这样使用：

# dblink is an object that knows how to connect to the database 
with dblink.CommittingSession() as session: 
    session.add(...) 
    # do anything else 
# at this point, session.commit() has been called 

或者：

try: 
    with dblink.CommittingSession() as session: 
    session.add(...) 
except ...: 
    # at this point, session.rollback has been called 
    log.error('We failed!') 

实施：

from contextlib import contextmanager 

class DbLink(object): 
    """This class knows how to connect to the database.""" 
    # ... 
    # Basically we wrap a sqlalchemy.orm.sessionmaker value here, in session_registry. 
    # You might want to create sessions differently. 

    @contextmanager 
    def CommittingSession(self, **kwargs): 
     """Creates a session, commits at the end, rolls back on exception, removes. 

     Args: 
     **kwargs: optional; supplied to session_registry while asking 
      to construct a session (mostly for testing). 

     Yields: 
     a session object. The session will .commit() when a `with SimpleSession()` 
     statement terminates normally, or .rollback() on an exception. 
     """ 
     try: 
     session = self.session_registry(**kwargs) # this gives us a session 
     # transaction has already begun here, so no explicit .begin() 
     yield session 
     except: 
     session.rollback() 
     raise 
     else: 
     session.commit() 
     finally: 
     # Note: close() unbinds model objects, but keeps the DB connection. 
     session.close() 
     self.session_registry.remove() 

Answer 2

您可以设计一个函数来管理错误句柄，您应该评估它们并考虑是否需要性能优化。

def commit_or_rollback(my_session, do_something, error_type): 
    try: 
     do_something(my_session) 
     my_session.commit() 
     return True 
    except error_type as err: 
     my_session.rollback() 
     print(err) 
     return False 

def do_something(my_session): 
    # do something 

commit_result = commit_or_rollback(my_session, do_something, NoResultFound) 

要小心会话控制和性能。这种方法可以保持代码清晰。