javascript中的链许诺 [英] chain promises in javascript

问题描述

为了在数据库中创建对象，我已经创建了许多类似的承诺.

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();
    });
  }
); 

最后，我要按我想要的顺序兑现我所有的诺言. (因为somes对象依赖于另一个对象，所以我需要保持顺序)

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)));

所以我希望看到:

User populated
Comment populated
Game populated
Room populated

不幸的是，此消息被打乱了，我不知道是什么.

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

谢谢

推荐答案

看起来像您理解了Promise错误，请重新阅读有关Promise的一些教程，以及此

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

使用new Promise(executor)创建承诺后，就会立即调用它，因此实际上所有功能都是在创建它们时执行的，而不是在链接它们时执行的.

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实际上应该是一个返回promise的函数，而不是promise本身. createComment，createGame，createRoom.

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

然后您就可以像这样将它们链接起来:

Then you will be able to chain them like this:

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

mongoose返回承诺的最新版本，如果您不传递回调，那么您不会不需要将其包装到一个返回诺言的函数中.

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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