在 sqlalchemy 函数中避免样板会话处理代码 [英] Avoiding boilerplate session handling code in sqlalchemy functions

问题描述

我有一个使用 sqlalchemy 的 python 应用程序，它有很多小型数据库访问功能.我试图避免在这些函数周围有大量样板会话处理代码.

I have a python application which has lots of small database access functions, using sqlalchemy. I'm trying to avoid having lots of boilerplate session handling code around these functions.

我有许多看起来像这样的函数:

I have numerous functions that look something like this:

def get_ticket_history(Session, ticket_id):
    s = Session()
    try:
        rows = s.query(TicketHistory)\
                .filter(TicketHistory.ticket_fk==ticket_id)\
                .order_by(TicketHistory.id.desc()).all()
        s.commit()
        return rows
    except:
        s.rollback()
        raise
    finally:
        s.close()

我正在尝试重构这些函数，但不确定我是否有最好的方法.我目前拥有的最好的是以下内容:

I am trying to refactor these functions, but not sure I have the best approach yet. The best I currently have is the following:

def execute(Session, fn, *args, **kwargs):
    s = Session()
    try:
        ret = fn(s, *args, **kwargs)
        s.commit()
        return ret
    except:
        s.rollback()
        raise
    finally:
        s.close()

def get_ticket_history(self, ticket_id):
    def sql_fn(s):
        return s.query(TicketHistory)\
                .filter(TicketHistory.ticket_fk==ticket_id)\
                .order_by(TicketHistory.id.desc()).all()
    return execute(self.sentinel_session, sql_fn)

有没有更好或更惯用的方法来做到这一点?也许使用装饰器?

Is there a better or more idiomatic way of doing this? Perhaps using a decorator?

谢谢，乔恩

推荐答案

SQLAlchemy 文档提供了一种使用上下文管理器执行此操作的可能方法.

The SQLAlchemy docs present a possible way of doing this with context managers.

http://docs.sqlalchemy.org/en/latest/orm/session_basics.html#when-do-i-construct-a-session-何时提交并何时关闭

为了完整起见，复制此处的代码片段:

Copying the code snippet here for completeness:

from contextlib import contextmanager

@contextmanager
def session_scope():
    """Provide a transactional scope around a series of operations."""
    session = Session()
    try:
        yield session
        session.commit()
    except:
        session.rollback()
        raise
    finally:
        session.close()

这个 session_scope 现在可以干净地使用，而无需重复样板.

This session_scope can be used cleanly without repeating the boiler plate now.

class ThingOne(object):
    def go(self, session):
        session.query(FooBar).update({"x": 5})

class ThingTwo(object):
    def go(self, session):
        session.query(Widget).update({"q": 18})

def run_my_program():
    with session_scope() as session:
        ThingOne().go(session)
        ThingTwo().go(session)

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