mysql - 如何从 Node.js 中运行 Mysql Select 的函数返回值

Question

我正在运行一个简单的程序进行长轮询，以检查数据库中是否发生任何更改，并将其发送到 Node.js 中的浏览器。我知道如何使用回调函数，但我需要从 program.query 函数返回一个值，因为我将在递归函数中使用它。感谢您的帮助。

var server=http.createServer(function(req,res){
    program.run(res, 5);
});

server.on('listening',function(){
    console.log('ok, server is running');
});

server.listen(9000);


var program = {

    run: function(res, id, old){

        if(old == undefined){
            // I need a value from database to be returned to old variable
            old = program.query(res, id /*, function(){res.end('there') }*/);
        }

        clearTimeout(tt);
        var tt = setTimeout( function(){

            // I need a value from database to be returned to new_ variable
            var new_ = program.query(res, id /*, function(){res.end('there') }*/);

            if(new_ != old){
                // ... Send Response with the change to browser
            }
            else{ // no change in database, so run again
                old = new_;
                program.run(res, id, old);
            }

        }, 2000);    

    },

    query: function(res, id /*,callback*/){

        connection.query('SELECT table1.column1 FROM table1 WHERE table1.id ="'+id+'"', function(err, rows, fields){


            //callback(res,id,rows[0].column1); // I don't want this solution
            return rows[0].column1; // Not working..

        });


    }

};

Answer 1

只需在回调中递归调用即可。它看起来和听起来一样:

var program = {

    run: function(res, id, old){

        if(old == undefined){
            program.query(res, id , function(res,id,result){
                old = result;

                clearTimeout(tt);
                var tt = setTimeout( function(){
                    program.query(res, id , function(res,id,new_){
                        if(new_ != old){
                            // ... Send Response with the change to browser
                        }
                        else{ // no change in database, so run again
                            old = new_;
                            program.run(res, id, old);
                        }
                        // not sure where you want to put the res.end()
                        // since I don't really know your logic.
                    });

                }, 2000);
            });
        }
        else {
            // This code is of course identical to the code above
            // so you can refactor it out into its own function.

            clearTimeout(tt);
            var tt = setTimeout( function(){
                program.query(res, id , function(res,id,new_){
                    if(new_ != old){
                        // ... Send Response with the change to browser
                    }
                    else{ // no change in database, so run again
                        old = new_;
                        program.run(res, id, old);
                    }
                    // not sure where you want to put the res.end()
                    // since I don't really know your logic.
                });

            }, 2000);
        }
    },

    query: function(res, id, callback){

        connection.query('SELECT table1.column1 FROM table1 WHERE table1.id ="'+id+'"', function(err, rows, fields){


            callback(res,id,rows[0].column1);    
        });


    }

};