python – 使用async / await打开/关闭数据库连接的最佳方法

在我发现的教程中,每个请求总是打开和关闭连接,例如：

import asyncio
import asyncpg

async def run():
    conn = await asyncpg.connect(user='user', password='password',
                             database='database', host='127.0.0.1')
    values = await conn.fetch('''SELECT * FROM mytable''')
    await conn.close()

loop = asyncio.get_event_loop()
loop.run_until_complete(run())

虽然这适用于单个功能,但Web应用程序如何？

IE：例如在Tornado中,每个URL都是一个类,这导致了很多类/方法.

我习惯以阻塞的方式打开连接,然后使用包装器进行异步数据库调用,并关闭连接只关闭服务器,在这种情况下使用async / await的最佳做法是什么？

解决方法:

如果没有使用asyncpg,我认为在大多数兼容asyncio的软件包中都有一个异步上下文管理器,可以准确地提供您所要求的内容.

就像是：

async with asyncpg.create_pool(**kwargs) as pool:
    async with pool.acquire() as connection:
        async with connection.transaction():
            result = await connection.fetchval(fetch stuff)
            connection.execute(insert stuff with result)

(摘自this question)

使用async with statements检查上下文管理器或示例的文档,或者如果没有其他内容,则检查源代码中已实现__aenter __,__ aexit__方法的类.

编辑1：

上面的例子部分取自我所链接的问题,部分是为了完整性而设计的.但是要解决你对with语句正在做什么的评论：

async with asyncpg.create_pool(**kwargs) as pool:
    #in this block pool is created and open
    async with pool.acquire() as connection:
        # in this block connection is acquired and open
        async with connection.transaction():
            # in this block each executed statement is in a transaction
            execute_stuff_with_connection(connection)
        # now we are back up one logical block so the transaction is closed
        do_stuff_without_transaction_but_with_connection(connection)
    # now we are up another block and the connection is closed and returned to the pool
    do_more_stuff_with_pool(pool)
# now we are up another level and the pool is closed/exited/cleaned up
done_doing_async_stuff()

我不确定这是多么好的解释,也许你应该在context managers读到.

标签：event-loop,python,async-await,tornado,asyncpg
来源： https://codeday.me/bug/20190910/1798530.html