javascript中的链式承诺 [英] chain promises in javascript

问题描述

为了在我的数据库中创建对象，我创建了许多这样的承诺.

var createUserPromise = new Promise(功能(解决，拒绝){用户创建({电子邮件:'[e-mail]'}， 功能() {console.log("用户填充");//创建用户时调用的回调解决();});});

最后，我想按照我想要的顺序调用我的所有承诺.(因为某些对象依赖于其他对象，所以我需要保持该顺序)

createUserPromise.then(createCommentPromise.then(createGamePromise.then(createRoomPromise)));

所以我希望看到:

用户填充评论已填充游戏已填充房间有人住

不幸的是，这条消息被洗牌了，我不明白是什么.

谢谢

解决方案

看起来你对 promises 理解有误，重新阅读一些关于 promises 的教程和这个 文章.

一旦您使用 new Promise(executor) 创建了一个 Promise，它就会立即被调用，因此您的所有函数实际上都是在您创建它们时执行的，而不是在您链接它们时执行.

createUser 实际上应该是一个返回承诺的函数而不是承诺本身.createComment、createGame、createRoom 也是.

然后你就可以像这样链接它们:

createUser().then(createComment).then(创建游戏).then(创建房间)

最新版本的 mongoose return promises 如果您不传递回调，那么您就不会'不需要把它包装成一个返回承诺的函数.

I've created many promises like that, in order to create object in my database.

var createUserPromise = new Promise(
  function(resolve, reject) {
    User.create({
      email: '[e-mail]'
    }, function() {
      console.log("User populated"); // callback called when user is created
      resolve();
    });
  }
); 

At the end, I want call all my promises in the order I want. (because somes object depend of other, so I need to keep that order)

createUserPromise
  .then(createCommentPromise
    .then(createGamePromise
      .then(createRoomPromise)));

So I expect to see :

User populated
Comment populated
Game populated
Room populated

Unfortunately, this messages are shuffled and I don't understand what.

Thanks

解决方案

Looks like you understood promises wrong, re-read some tutorials on promises and this article.

As soon as you create a promise using new Promise(executor), it is invoked right away, so all your function actually are executed as you create them and not when you chain them.

createUser actually should be a function returning a promise and not a promise itself. createComment, createGame, createRoom too.

Then you will be able to chain them like this:

createUser()
.then(createComment)
.then(createGame)
.then(createRoom)

Latest versions of mongoose return promises if you don't pass callbacks, so you don't need to wrap it into a function returning a promise.

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