Javascript 执行查询时返回未定义的对象

我正在Node.js上构建一个应用程序，通过mongoose与MongoDB一起工作。连接是完美的，我可以添加新的文件，问题绝对不是在连接

我正在一个单独的.js文件中构建所有与mongoose一起工作的函数，我从dbconfig.js调用了这个文件

dbconfig.js

const mongoose = require('mongoose');

// Models
const User = require('./models/User');
const Category = require('./models/Category');

var database_name = "htm";
mongoose.Promise = global.Promise;

// Connection with database_name
var connect = () => {
    mongoose.connect("mongodb://localhost/"+database_name, {useNewUrlParser: true}).then(() =>{
        console.log("Conectado ao database: " + database_name);
    }).catch((erro) => {
        console.log("Erro ao se conectar ao database: " + database_name +" - "+ erro);
    });

    mongoose.model('users', User);
    mongoose.model('categories', Category);
}

var getCategory = () => {
    const Ref = mongoose.model('categories');
    Ref.find().then((categories) => {
        return categories;
    })
}

module.exports = {
    connect: connect,
    getCategory: getCategory
}

const express = require('express');
const app = express();
const categoriesRouter = require('./routes/categories');
const handlebars = require('express-handlebars');
const path = require('path');
const configDB = require('./dbconfig')

// Config
    // Template Engine
        app.engine('handlebars', handlebars({defaultLayout: 'main'}));
        app.set('view engine', 'handlebars');

    // Start Database Connection
        configDB.connect();

    // Public
        app.use(express.static(path.join(__dirname, "public")));

// Routes
    app.use('/categorias', categoriesRouter);

    app.get('/', (req, res) => {
        var categories = configDB.getCategory();

        res.render('home', categories);

    });

app.listen(3001, () =>{
    console.log("Servidor iniciado na porta 3001");
});

问题在于getCategory（）函数，当我在我的app.js（这个项目节点的主文件）中调用它时，它只返回未定义的。我知道变量类别是填写的，因为我插入了

console.log（categories）

并得到以下结果：

[ { _id: 5c7ea6fb91526418ec3ba2fd,
    name: 'UNHAS',
    slug: 'unhas',
    __v: 0 } ]

app.js

const mongoose = require('mongoose');

// Models
const User = require('./models/User');
const Category = require('./models/Category');

var database_name = "htm";
mongoose.Promise = global.Promise;

// Connection with database_name
var connect = () => {
    mongoose.connect("mongodb://localhost/"+database_name, {useNewUrlParser: true}).then(() =>{
        console.log("Conectado ao database: " + database_name);
    }).catch((erro) => {
        console.log("Erro ao se conectar ao database: " + database_name +" - "+ erro);
    });

    mongoose.model('users', User);
    mongoose.model('categories', Category);
}

var getCategory = () => {
    const Ref = mongoose.model('categories');
    Ref.find().then((categories) => {
        return categories;
    })
}

module.exports = {
    connect: connect,
    getCategory: getCategory
}

const express = require('express');
const app = express();
const categoriesRouter = require('./routes/categories');
const handlebars = require('express-handlebars');
const path = require('path');
const configDB = require('./dbconfig')

// Config
    // Template Engine
        app.engine('handlebars', handlebars({defaultLayout: 'main'}));
        app.set('view engine', 'handlebars');

    // Start Database Connection
        configDB.connect();

    // Public
        app.use(express.static(path.join(__dirname, "public")));

// Routes
    app.use('/categorias', categoriesRouter);

    app.get('/', (req, res) => {
        var categories = configDB.getCategory();

        res.render('home', categories);

    });

app.listen(3001, () =>{
    console.log("Servidor iniciado na porta 3001");
});

无论何时在my app.js中收到变量类别，它都以未定义的形式到达

---

有人能帮我吗？

您在express路由器中没有正确使用从

getCategory（）

返回的

Promise

对象：

    app.get('/', (req, res) => {
        var categories = configDB.getCategory(); <-- this is a Promise, not a synchronous value
        res.render('home', categories);
    });

---

受到@jakemingolla建议使用asyncwait的回复的启发，我开始使用callback返回“categories”对象，一切都很顺利

函数在我的文件dbconfig.js中

const getCategoryList = (callback) => {
    CategoryRef.find().then((categories) => {
        callback(categories);
    })
}

调用my app.js文件中的函数

app.get('/', (req, res) => {
    database.getCategoryHomeList((categories) => {
        res.render('home', {categories: categories});
    })
});

---

这对我来说不起作用，但它激励我带着承诺工作并解决问题