在承诺中包含一个反模式的承诺吗？ [英] Is wrapping a promise in a promise an anti-pattern?

问题描述

我正在尝试使用Promise API编写重新连接到数据库的代码，并使用Promise API进行超时。

我最终做的是将承诺包装到在承诺中连接到DB，但我不确定这是否是最好的做事方式。我认为可能有一种方法可以使用原始承诺来尝试连接到数据库，但我无法弄明白。

  function connect（resolve）{
 console.log（'Connecting to db ...'）; 
 MongoClient.connect（url，{promiseLibrary：Promise}）
 .then（（db）=> resolve（db））
 .catch（（err）=> {
 console.log（'db connection failed！：\ n'，err）; 
 if（retry ++< 3）{
 console.log（'再试一次......'）; 
 setTimeout（（）=> connect（resolve），5000）; 
} else {
 console.log（'达到重试限制！'）; 
} 
 }）; 
} 
 
 module.exports = new Promise（connect）; 
  

我认为没有 setTimeout 阻止，但我无法解决它。

解决方案

这是一个稍微更通用的解决方案：

  function withRetry（asyncAction，retries）{
 if（retries === 0）{
 // Promise.resolve to conversion同步引发拒绝。 
返回Promise.resolve（）。then（asyncAction）; 
} 
返回Promise.resolve（）
 .then（asyncAction）
 .catch（（）=> withRetry（asyncAction，retries  -  1））; 
} 
  

此函数将采用一个函数返回一个promise和多次重试，如果Promise拒绝，则重试该函数的次数为 retries 。

如果它结算，则重试在你的情况下：

 让connectionPromise = withRetry （连接，3）; //如果失败则连接3次重试
  

I was trying to write code for reconnecting to a database with a timeout using a Promise API.

What I ended up doing in the end was wrapping the promise to connect to the DB in a promise, but I'm not sure if that's the best way to do things. I thought there might be a way to use the original promise from trying to connect to the db, but I couldn't figure it out.

function connect(resolve) {
  console.log('Connecting to db...');
  MongoClient.connect(url, { promiseLibrary: Promise })
    .then((db) => resolve(db))
    .catch((err) => {
      console.log('db connection failed!:\n', err);
      if (retry++ < 3) {
        console.log('Trying again...');
        setTimeout(() => connect(resolve), 5000);
      } else {
        console.log('Retry limit reached!');
      }
    });
}

module.exports = new Promise(connect);

I think it would be possible without the setTimeout block, but I couldn't work around it.

解决方案

Here's a slightly more general solution:

function withRetry(asyncAction, retries) {
  if (retries === 0) {
    // Promise.resolve to convert sync throws into rejections.
    return Promise.resolve().then(asyncAction); 
  }
  return Promise.resolve()
    .then(asyncAction)
    .catch(() => withRetry(asyncAction, retries - 1));
}

This function will take a function that returns a promise, and a number of retries, and retry the function as many times as retries, if the Promise rejects.

If it resolves, the retry chains stops.

In your case:

let connectionPromise = withRetry(connect, 3); // connect with 3 retries if fails.

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