Thinking about Nodejs access to MySQL

Nodejs to access the MySQL database, you must first install the package mysql, command: npm install MySQL. After successful installation, the following database code is accessed:

varMySQL = require (' MySQL ');varOptions ={host:' 172.23.88.107 ', Port:3306, Database:' Test ', User:' Root ', Password:' Zdsoft '};varPool =mysql.createpool (options);p ool.getconnection (function(ERR, conn) {if(Err) {Console.log (err);//Printing error Messages}Else{conn.query ("SELECT * FROM Student",NULL,function(Err, results, fields) {//Release Connectionconn.release (); if(Err) {Console.log (err); } Else{Console.log (results);//successful, print result set            }        })    }});

OK, the above code has been tested there is no problem, but now there is a problem, every time we access the database is written so large a feeling too tired, so we want to extract the public part to create a class, the file name is: Sqlhelper.js. Since database access is asynchronous, we cannot directly return by returning it, so we have to use the callback function, and the Sqlhelper.js code is as follows:

varMySQL = require (' MySQL ');varOptions ={host:' 172.23.88.107 ', Port:3306, Database:' Test ', User:' Root ', Password:' Zdsoft '};varPool =mysql.createpool (options); Exports.query=function(SQL, Vals, fn) {pool.getconnection (function(ERR, conn) {if(Err) {fn (NewError (err)); } Else{conn.query (SQL,NULL,function(Err, results, fields) {//Release Connectionconn.release (); if(Err) {fn (NewError (err)); } Else{fn (NULL, results, fields); }            })        }    });}

In this way, we can directly pass the call to the FN callback function, the method is called as follows:

var mysql = require ('./lib/sqlhelper.js '); // sqlhelper.js file below the Lib folder var NULL function (Err, results, fields) {    if  (results) {        for (Let index = 0; index < res Ults.length; index++) {            console.log (results[index].name);        }     Else {        console.log ("err,msg:" + err);    });

Since then, we have also been the most accomplished.

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However, we have another way to achieve this, through the Promise object, through the Promise object we can write the same as the synchronous program to write asynchronous code, so do not have to go to an infinite number of nested callback functions, Sqlhelper.js modified as follows:

varMySQL = require (' MySQL ');varOptions ={host:' 172.23.88.107 ', Port:3306, Database:' Test ', User:' Root ', Password:' Zdsoft '};varPool =mysql.createpool (options); Exports.query=function(SQL) {return NewPromise (function(Resolve, Reject) {pool.getconnection (function(ERR, conn) {if(Err) {reject (err);//let the state become defunct and pass the error message back}Else{conn.query (SQL,NULL,function(Err, results, fields) {//Release Connectionconn.release (); if(Err) {reject (err); } Else{Resolve (results, fields);//let the state become successful and pass the success data back                    }                })            }        }); });}

The calling method is modified as follows:

var mysql = require ('./lib/sqlhelper.js '); // sqlhelper.js file below the Lib folder var promise = Mysql.query ("SELECT * from Student");p romise.then (function  (results, Fields) {    for (Let index = 0; index < results.length; index++) {        Console.log (results[ Index].name);     function (Err) {    console.log (err);});

As you can see, we're not using a callback function anymore.

Thinking about Nodejs access to MySQL