Sequelize纯对象返回空-大括号行为不正常

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，我注意到当我用大括号包围message.get方法时，它停止了正常工作。

有人能解释一下为什么会发生这种情况吗？通过用大括号包围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)。

原始代码：

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 Filesnodejsnode.exe" C:UsersgiannDropboxIdeaProjectsHomework14-Tech-Blogserver.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，我去掉了花括号块：

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 Filesnodejsnode.exe" C:UsersgiannDropboxIdeaProjectsHomework14-Tech-Blogserver.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

它的语法(熟记)

(x) => x

相当于

(x) => {
return x;
}

如果你不把退货单放在第二种形式，你就没有退货单，这意味着它将返回undefined。因此你看到了什么。

在你的例子中，这应该工作

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