如何从 node.js 中的 mysql SELECT 查询返回值 [英] How to return a value from a mysql SELECT query in node.js
问题描述
我对 Node.js 还是很陌生,我正在尝试了解回调是如何工作的.所以,这是我的问题:
I'm still very new to Node.js, and i'm trying to understand how callbacks work. So, here is my problem :
我应该放更多代码:
发布:
app.post('/register', function(req, res) {
//get data from the request
var data = {
username: req.body.username,
email: req.body.email,
password: req.body.password
};
function fetchID(callback) {
connection.query('SELECT id_user FROM USERS WHERE username = ?', data.username, function(err, rows) {
if (err) {
callback(err, null);
} else
callback(null, rows[0].id_user);
});
}
var user_id;
fetchID(function(err, content) {
if (err) {
console.log(err);
return next("Mysql error, check your query");
} else {
user_id = content;
console.log(user_id); //undefined
}
});
console.log(user_id); //undefined
var payload = {
iss: req.hostname,
sub: user_id
}
console.log(payload.sub); //correct id
})
获取:
app.get('/todos', function(req, res) {
if (!req.headers.authorization) {
return res.status(401).send({
message: 'You are not authorized !'
});
}
var token = req.headers.authorization.split(' ')[1];
var payload = jwt.decode(token, "shhh..");
//additional level of security
console.log('sub id is : ' + payload.sub); //undefined
if (!payload.sub) {
return res.status(401).send({
message: 'Authentication failed !'
});
}
})
我对每个 console.log 进行了注释以使其更加清晰.当我在 app.get()
I commented each console.log to be more clear. I need to get the correct id when i check for if (!payload.sub)
in app.get()
推荐答案
你的两个函数应该是这样的 -
Your two functions should be something like -
function fetchID(data, callback) {
connection.query('SELECT id_user FROM USERS WHERE username = ?', data.username, function(err, rows) {
if (err) {
callback(err, null);
} else
callback(null, rows[0].id_user);
});
}
然后
var user_id;
fetchID(data, function(err, content) {
if (err) {
console.log(err);
// Do something with your error...
} else {
user_id = content;
}
});
在回调函数中,返回的变量content
将保存user_id
的值.
Here in the callback function, the returned variable content
will hold the value for user_id
.
编辑
我还没有解决你上面描述的确切问题.
I have not solved the exact problem as you had described above.
但是在下面的例子中,我已经证明了回调机制是有效的 -
But in following example, I have shown that, the callback mechanism is working -
首先(创建表格并插入一些虚拟数据)-
use test;
create table users (id int(11) primary key,username varchar(100));
insert into users values(1, "John");
insert into users values(2, "Sham");
现在我已经将您的 post 方法设置为 get 并在浏览器中进行了测试.
Now I have made your post method as get and tested in browser.
以下是在我的本地主机中测试的完整类 -
Following is the full class tested in my localhost -
var application_root = __dirname,
express = require("express"),
mysql = require('mysql');
var app = express();
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
password : 'admin',
database: "test"
});
app.get('/getuser', function(req, res) {
//get data from the request
var data = {
username: req.query.username
};
function fetchID(data, callback) {
connection.query('SELECT id FROM users WHERE username = ?',
data.username, function(err, rows) {
if (err) {
callback(err, null);
} else
callback(null, rows[0].id);
});
}
var user_id;
fetchID(data, function(err, content) {
if (err) {
console.log(err);
res.send(err);
// Do something with your error...
} else {
user_id = content;
console.log(user_id);
res.send("user id is -" + user_id);
}
});
})
app.listen(1212);
现在这些请求将产生这个输出——http://127.0.0.1:1212/getuser?username=john
=> user id is -1
和http://127.0.0.1:1212/getuser?username=sham
=> user id is -2
Now these requests will produce this output -
http://127.0.0.1:1212/getuser?username=john
=> user id is -1
and
http://127.0.0.1:1212/getuser?username=sham
=> user id is -2
希望这个代码示例能帮助你理解 node.js 中的回调.
Hope this code example will help you to understand the callback in node.js.
谢谢
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