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。
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.
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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