mongoDB承诺过早归还 [英] mongoDB promise gets returned too early

问题描述

我刚刚开始尝试在Node.js应用程序上实现Promises.现在，我正在检查用户名和密码是否存在，然后使用mongodb来查找未找到用户的用户和密码，它会设置promise.reject()，但它返回的promise太早了，它仍然处于未决状态.如果有人可以帮助或给我有关如何重构的想法，将不胜感激.

I just started trying to implement Promises on my Node.js app. Right now i'm checking if a user and password exists then using mongodb to look them up if user isn't found it sets promise.reject() but it is returning the promise too early and it's still in the pending state. If anyone can help or give me ideas on how to refactor it would be much appreciated.

https://gist.github.com/joshbedo/8957056

推荐答案

这是预期的行为，它在仍处于挂起状态时会返回promise.

It is the expected behavior it returns the promise while it is still in the pending state.

您应使用then()检查承诺解决方案.

You should use then() to check for promise resolution.

另一件事是，在开始使用Promise时，您不应该使用传统的mongo接口，而应使用Collection原型的所有方法，因此您可以返回由mongo find方法及其链条创建的Promise.然后.否则，我看不到使用诺言的意义.您的方式不会减少您必须编写的代码量.

Another thing is that you should not use the traditional mongo interface when starting to work with promises, but rather promisify all method of the Collection prototype, so you can return the Promise created by the mongo find method with its chain of thenable. Otherwise I don't see the point of using promises. The way you do does not reduce the amount of code you have to write.

顺便说一句，恕我直言，您应该使用bluebird而不是Q，因为它是目前唯一不会非常慢的promise库.

By the way, IMHO you should use bluebird rather than Q, as it is at the moment the only promise library which is not extremely slow.

示例:

在db.js中

var mongoClient = require('mongodb').MongoClient;
var collection  = require('mongodb').Collection;

var Promise     = require('bluebird');

// We promisify everything. Bluebird add ***Async function which return promises.
Promise.promisifyAll(collection.prototype);
Promise.promisifyAll(mongoClient);

//In mongodb cursor is not built from protoype I use to promisify it each time. Not necessary if you don't use cursors.
collection.prototype._find = collection.prototype.find;
collection.prototype.find = function() {
  var cursor = this._find.apply(this, arguments);
  cursor.toArrayAsync = Promise.promisify(cursor.toArray, cursor);
 return cursor;
};

//then you connect to the DB and exports your collections...

在其他地方，以您的示例为例:

elsewhere, taking your example :

this.loginUser = function(user) {
  var userid = user.userid,
  var password = (user.password) ?
    crypto.createHash("md5").update(user.password).digest("hex"):
    undefined
  var rememberme = user.rememberme;

  if(userid && password) {
    // we directly return the promise from mongodb, that we chain with a then
    return db.users.findOneAsync({ email: userid, password: password }) // return a promise that we chain
    .then(function(user) { // that we chain
      if(user) {
        var logincode = uuid.v4(),
        var token = jwt.encode({email: userid, password: password}, secret);

        if(rememberme) {
          res.cookie("clogincode", logincode, { magAge: 900000 } );
        }
        return user;  // return in a then callback will just resolve the promise
      } else {
        throw  new Error('User not found'); // throwing in a then callback will just reject the promise
      }
    }); // end of the then, then return a promise that we return (with the return keyword above)
  } else {
    return Promise.reject("Username or Password was not entered"); // this is the only case where we have to actually create a promise ourself
  }
}

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