如何从nodejs中的另一个文件回调函数？

Question

我开始使用异步编程,我正在创建一个nodejs应用程序,我在一些文件中切片代码:index.js,ctlUser.js,DAO.js等... .. Index.js是它需要的主文件ctlUser和ctlUser需要DAO.js ... DAO连接数据库并执行查询...

抽象,我的结构是这样的......

Index.js

var ctlUser =  require('./ctlUser.js');
var username = ctlUser.getUserName('1');
console.log("Return from ctlUser" + username);

ctlUser.js

var DAO = require('./DAO.js');
var getUserName = function(id){
    var userName = DAO.executeQuery("SELECT username FROM tbUsers WHERE id = " + id );
    console.log(Return from DAO = userName);
    return username;
}

DAO.js在这里一切都很好......

var mysql      = require('mysql'); 
var executeQuery = function(query) {    
        var connection = mysql.createConnection({
            host        : SERVER,
            user        : USER,
            password    : PASSWORD,
            database    : DATABASE
        });
        connection.connect();
        connection.query(query, function(err, rows, fields) {
            if (err) throw err;
            connection.end();
            console.log("Here in DAO: " + rows[0].username);
            return rows[0].username;
        });
    };

输出$ node index.js是:

Return of ctlUser: undefined
Return of DAO: undefined
Here in DAO: Filipe Tagliacozzi

我抽象所有模块导出everithing工作正常固定变量,但数据库响应不..如何在此结构中实现回调,以将userName带到index.js？

Answer 1

更改DAO.js模块中的executeQuery函数以使用回调:

var executeQuery = function(query,callback) {    
        var connection = mysql.createConnection({
            host        : SERVER,
            user        : USER,
            password    : PASSWORD,
            database    : DATABASE
        });
        connection.connect();
        connection.query(query, function(err, rows, fields) {
            if (err) throw err;
            connection.end();
            console.log("Here in DAO: " + rows[0].username);
            callback(rows[0].username);
        });
    };

通过ctlUser.js中的getUserName函数链接回调:

    var getUserName = function(id,callback){
        DAO.executeQuery("SELECT username FROM tbUsers WHERE id = " + id ,function(username){
           console.log("Return from DAO =" ,userName);
           callback(username);
        });       
    }

然后在index.js中使用它,如下所示:

var ctlUser =  require('./ctlUser.js');
ctlUser.getUserName('1',function(username){
    console.log("Return from ctlUser" + username);
});