javascript - 返回 null mysql nodejs

Question

请查看 dbfn.js 文件

/*database function file;*/

var db = require('./connection');

function check_conn(){
    if(db){
        console.log('We are connected to Database server'.bgGreen);
        return true;
    }else{
        console.log('We are not connected to DataBase server'.bgRed);
        return false;
    }
}

module.exports = {

    testCon : function(){
        if(check_conn() === true){
            return 'We are connected to DB';
        }else return 'We are not connected to DB';
    },

    get_user : function(){
        db.query('SELECT * FROM users',function(err,results,fields){
            if(err){
                console.log(err)
                return err;
            }
            if(results){
                console.log(results);
                return results;
            }
            console.log('nothing...');
        });
    }
};

现在，查看routes.js 文件

var db = require('./dbfn');

module.exports = function(app){

    /*
        Routing starts here
    */

    //root route
    app.get('/', function(req, res){
        res.render('index.ejs');
    });

    //test route
    app.get('/test',function(req,res){

        var x = db.get_user();
        console.log(x);
        res.writeHead(200, {'Content-Type': 'text/json'});
        res.json(x);
    });



    //default it should stay at bottom
    app.get('*',function (req, res) {
        //res.redirect('/');
        res.send(404);
    });
}

dbfn 文件上的 console.log 写入来自 MySQL 数据库的完整对象，但是当我在 paths.js 文件上调用它作为 var x it null 时，我真的不明白我实际上如何克服这个问题。是的，我是 NodeJs 的新学生

谢谢。

Answer 1

您无法从同步函数内的异步调用返回。相反，您需要将回调传递给 get_user()，如下所示:

dbfn.js

var db = require('./connection');

function check_conn(){
    if(db){
        console.log('We are connected to Database server'.bgGreen);
        return true;
    }else{
        console.log('We are not connected to DataBase server'.bgRed);
        return false;
    }
}

module.exports = {

    testCon : function(){
        if(check_conn() === true){
            return 'We are connected to DB';
        }else return 'We are not connected to DB';
    },

    get_user : function(cb){
        db.query('SELECT * FROM users',function(err,results,fields){
            if(err){
                console.log(err)
                cb(err);
            }
            if(results){
                console.log(results);
                cb(null, results);
            }
            console.log('nothing...');
        });
    }

};

routes.js

var db = require('./dbfn');

module.exports = function(app){

    /*
        Routing starts here
    */

    //root route
    app.get('/', function(req, res){
        res.render('index.ejs');
    });

    //test route
    app.get('/test',function(req,res){

        db.get_user(function(err, response) {
            if(err) {
                // handle error
            }
            else {
                var x = response;
                console.log(x);
                res.writeHead(200, {'Content-Type': 'text/json'});
                res.json(x);
            }
        });

    });

    //default it should stay at bottom
    app.get('*',function (req, res) {
        //res.redirect('/');
        res.send(404);
    });
}

现在，回调中的代码仅在数据库查询完成后才会触发。