不使用回调时的结果不确定。Nodejs，Express和SQL Server Express

phil o.O 发表于 Dev

菲尔

以下问题由mssql，Nodejs，Gulp，Express和SQL Server Express组成。我能够成功登录到SQL Server Express。但是，当我使用不带callback的bookRoute.js代码片段时，返回值是不确定的。但是，当我使用回调时，我得到了数据。但是，我不明白为什么。

app.js代码段：

var config = {
    user: 'user',
    password: 'password',
    server: 'localhost',
    database: 'Books',
    options: {
       instance: 'SQLEXPRESS'
    }
};

sql.connect(config, function(err){
    console.log(err);
});

没有回调的bookRoute.js代码段：

bookRouter.route('/')
.get(function (req, res) {
    console.log('book router');
    var request = new sql.Request();
    request.query('select * from books').then(
        function (err, recordset) {
            console.log(recordset);
        })
    .catch(function(err){  console.log(err)});
    });

带有回调的bookRoute.js代码段：

bookRouter.route('/')
.get(function (req, res) {
    console.log('book router');
    var request = new sql.Request();
    request.query('select * from books',
        function (err, recordset) {
            console.log(recordset);
        });
});

用户访问网页后，控制台应显示结果。不幸的是，不使用回调时，显示的唯一结果是不确定的。

控制台输出：

P:\ub\lic\library>gulp serve
[11:08:28] Using gulpfile P:\ub\lic\library\gulpfile.js
[11:08:28] Starting 'style'...
[11:08:28] Starting 'inject'...
[11:08:53] Finished 'inject' after 808 ms
[11:08:53] Finished 'style' after 25 s
[11:08:53] Starting 'serve'...
[11:08:53] Finished 'serve' after 5.31 ms
[11:08:53] [nodemon] 1.9.2

[11:08:53] [nodemon] to restart at any time, enter `rs`
[11:08:53] [nodemon] watching: *.js src/**/*.js
[11:08:53] [nodemon] starting `node app.js`

running server on port 3000
null
book router
undefined
[11:09:21] [nodemon] restarting due to changes...
Restarting the server.....beep boop beep beep
[11:09:21] [nodemon] restarting due to changes...
Restarting the server.....beep boop beep beep
[11:09:21] [nodemon] starting `node app.js`
running server on port 3000
null
book router
[ { id: 1,
    title: 'A,B,C with Big Bird           ',
    author: 'Michael Jacob ' },
  { id: 2,
    title: 'Peter and his Petunias        ',
    author: 'Jess Holiday  ' },
  { id: 3,
    title: 'The Amazing Average Guy       ',
    author: 'Don Dillon    ' } ]

用户名

没有回调的bookRoute.js代码段：

bookRouter.route('/').get(function (req, res) {
console.log('book router');
var request = new sql.Request();
request.query('select * from books')
    .then(function (recordset) {
        console.log(recordset);
    })
    .catch(function (err) {
        console.log(err);
    });
});

当使用不带回调的bookRoute.js代码片段时，该then函数应仅包含一个参数，该参数是查询的结果，即文档中所述的方式。出现错误时，catch将调用该函数。

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