Sequelize 普通对象返回空 - 花括号行为不端

Question

场景： 当我试图从 sequelize 查询中获取一个普通对象时，我得到了一组 3 个空对象。

解决方案： 经过几个小时的尝试，我注意到当我用花括号包围 message.get 方法时，它会停止正常工作。

有人能解释一下为什么会这样吗？通过用花括号包围 message.get({plain:true}) 方法，它给出了一组空对象（在这种特殊情况下为 3 个空对象）。

原代码：

const router = require('express').Router();
const {Message} = require('../models/');


router.get('/', async (req, res) => {
    try {

        const dbMessagesData = await Message.findAll();

        // HERE *****************************************
        const messages = dbMessagesData.map(message => {
                message.get({plain: true});
            }
        );


        // MESSAGES CONTENT
        messages.forEach(( element , index, array)=>{
             console.log("---> element :" + JSON.stringify (element) );
        });

        res.render('homepage', {messages});
    } catch
        (e) {
        res.status(400).send(e.message);
    }
});

module.exports = router;

终端：

"C:\Program Files\nodejs\node.exe" C:\Users\giann\Dropbox\IdeaProjects\Homework\14-Tech-Blog\server.js
(node:97384) [SEQUELIZE0002] DeprecationWarning: The logging-option should be either a function or false. Default: console.log
(Use `node --trace-deprecation ...` to show where the warning was created)
Server listening on port 3000
Executing (default): SELECT `id`, `title`, `content`, `created_at` AS `createdAt`, `updated_at` AS `updatedAt`, `user_id`, `user_id` AS `UserId` FROM `Message` AS `Message`;
---> element :undefined
---> element :undefined
---> element :undefined

现在，我把花括号块去掉了：

const router = require('express').Router();
const {Message} = require('../models/');


router.get('/', async (req, res) => {
    try {

        const dbMessagesData = await Message.findAll();

        //HERE - curly braces removed ****************
        const messages = dbMessagesData.map(message => 
                message.get({plain: true})
            
        );


        // MESSAGES CONTENT
        messages.forEach(( element , index, array)=>{
             console.log("---> element :" + JSON.stringify (element) );
        });

        res.render('homepage', {messages});
    } catch
        (e) {
        res.status(400).send(e.message);
    }
});

module.exports = router;

终端：

"C:\Program Files\nodejs\node.exe" C:\Users\giann\Dropbox\IdeaProjects\Homework\14-Tech-Blog\server.js
(node:188548) [SEQUELIZE0002] DeprecationWarning: The logging-option should be either a function or false. Default: console.log
(Use `node --trace-deprecation ...` to show where the warning was created)
Server listening on port 3000
Executing (default): SELECT `id`, `title`, `content`, `created_at` AS `createdAt`, `updated_at` AS `updatedAt`, `user_id`, `user_id` AS `UserId` FROM `Message` AS `Message`;
---> element :{"id":1,"title":"Title 1","content":"Hey, this is the first message","createdAt":"2021-08-23T17:29:56.000Z","updatedAt":"2021-08-23T17:29:56.000Z","user_id":1,"UserId":1}
---> element :{"id":2,"title":"Title 2","content":"Hey, this is the second message","createdAt":"2021-08-23T17:29:56.000Z","updatedAt":"2021-08-23T17:29:56.000Z","user_id":2,"UserId":2}
---> element :{"id":3,"title":"Title 3","content":"Hey, this is the third message","createdAt":"2021-08-23T17:29:56.000Z","updatedAt":"2021-08-23T17:29:56.000Z","user_id":3,"UserId":3}
``````

What am I missing here?? 

Answer 1

它只是语法（记住它）

(x) => x

等价于

(x) => {
 return x;
}

如果您不将退货放在第二个表格中，您将没有退货，这意味着 它将返回未定义。因此你所看到的。

在你的例子中这应该可以工作

const messages = dbMessagesData.map(message => {
                return message.get({plain: true});
            }
        );