承诺并等待Javascript

Question

I've got a strange problem.. FIrst, take a look at my code:

This one is where I use my await..

case "detail": {
                const lineMessages = [];
                let item = await this.getItem(postback.id);
                let lineMessage = {
                        type: "text",
                        text: item.longDesc
                };
                lineMessages.push(lineMessage);
                return new Promise(function(resolve, reject) {
                    if(lineMessages != []) {
                        resolve(lineMessages);
                    }
                    else {
                        let error = new Error("Cannot catch item ${postback.id}");
                        reject(error);
                    }
                });

This is the getItem(id) method..

    getItem(id) {
    return Item.find({_id: id}).exec();
}

But it turns out the text key on my lineMessage is undefined..
Then, the lineMessage is LineMessages: [{"type":"text"}] ( I once logged it on my console)
Why await doesn't stop the execution in my case?
It seems it tries to look up item.longDesc before item is resolved (just my guess tho).
Please help

Answer 1

When you require mongoose you can pass native es6 Promise to mongoose options, then you can use native promises instead of mongoose queries

const mongoose = require('mongoose');
mongoose.Promise = Promise; // or you can use bluebird. Add this line in models and before connection to database

Item.find({_id: id}).exec() // shoud return native Promise 

Or on mongoose connection options (globally)

const options = {
    promiseLibrary: global.Promise
};
mongoose.connect(uri, options);

http://mongoosejs.com/docs/connections.html

Mongoose queries is pretty weird. Item.find({_id: id}).exec() returs mongoose query, and have .then() method, but its not native js promise! When you add custom promiseLibrary to mongoose instance then Item.find({_id: id}).exec() returns native js Promise and work with async await.

Answer 2

事实证明，猫鼬findOne()返回一个具有单个对象的数组，而不仅仅是一个对象。