var mysql = require('mysql');
var con = mysql.createConnection({
host: "host",
user: "login",
password: "password",
database: "db"
});
con.connect(function (err) {
if (err) throw err;
console.log("Connected!");
function addTalentPoint(id,amount){
var sql = "SELECT RegValue FROM `Registry` WHERE RegChaId="+id+" AND RegIdentifier='TalentPoints'"
var endingTalentPoint = 0;
con.query(sql, function (err, result) {
if (err) throw err;
console.log("Starting Talent Point: "+result[0].RegValue);
endingTalentPoint = result[0].RegValue + amount
var sql = "UPDATE `Registry` SET RegValue="+endingTalentPoint+" WHERE RegChaId="+id+" AND RegIdentifier='TalentPoints'"
con.query(sql, function (err, result) {
if (err) throw err;
console.log(endingTalentPoint)
});
});
}
function getTalentPoint(id){
var sql = "SELECT RegValue FROM `Registry` WHERE RegChaId="+id+" AND RegIdentifier='TalentPoints'"
con.query(sql, function (err, result) {
if (err) throw err;
console.log("get talent point: "+result[0].RegValue);
});
}
addTalentPoint(4,5)
getTalentPoint(4)
});
My example output:
Starting Talent Point: 125
get talent point: 125
130
I have read through numerous blogs and tried using async / await and setting up promises but I'm not getting where I need to be. I'm trying to get the code to wait for addTalentPoint to finish before getTalentPoint executes. Is it just the nature of the beast that it sends the query off, and then continues on with the code? I could put getTalentPoint inside the callback under the UPDATE, but how can I know the update finished?
addTalentPoint is still doing async stuff - all those con.query calls are async - so unless you do the work in the callbacks, things will just be executed immediately (like your getTalentPoint function) - one solution would be to add a callback function to the addTalentPoint function. See the below changes:
//First, add a callback parameter
function addTalentPoint(id,amount,callback){
...
//next, use this callback when the work is done
if (err) throw err;
console.log(endingTalentPoint)
if (callback) callback(); //if a callback exists, call it
Now, use your new param:
addTalentPoint(4,5, function() {
//All done doing the work in addTalentPoint, lets do more things now!
getTalentPoint(4)
})
Related
In my project, I access the MySQL database. I can call and run queries in this database through the program. However, after a while, the called queries become dysfunctional or not called at all.
The example run of the queries:
When I investigated my problem, I found a solution that I needed to increase the maximum number of connections. However, even if I used it, there was no change.
I tried this code: SET GLOBAL max_connections = 150; from this source.
The connection part via node.js:
const connection = mysql.createPool({
host : '192.168.1.101',
user : 'db_manager',
password : '...',
database : 'venue_recommendation'
});
const app = express();
app.get('/venues', function (req, res) {
let sQuery = "SELECT * FROM mekanlar WHERE mekanlar.mahalle_no=\""+req.query.neig+"\" AND mekanlar.puan >="+req.query.star+" AND mekanlar.fiyat <="+req.query.price+";"
console.log(">>>>>",sQuery)
connection.getConnection(function (err, connection) {
if(err) throw err;
connection.query(sQuery, function (error, results, fields) {
if (error) throw error;
res.send(results);
});
});
});
app.get('/Cuisines', function (req, res) {
let sQuery = "SELECT * FROM mutfaklar;"
console.log(">>>>>",sQuery)
connection.getConnection(function (err, connection) {
if(err) throw err;
connection.query(sQuery, function (error, results, fields) {
if (error) throw error;
res.send(results);
});
});
});
I've been using mountebank to do some stubbing for performance testing and its an awesome tool. The functional teams have asked if it can be repurposed to support functional testing and I'd said i'd have a look.
What I want to achieve is to select from a mysql database an account number and its account balance and then return the balance to the client (in this case a jmeter harness)
function (request, state, logger) {
logger.info('GBG - getAccountBalance');
var mysql = require('mysql');
var result = '';
var con = mysql.createConnection({
host: "localhost",
user: "user",
password: "password",
database: "customer"
});
con.connect(function(err) {
if (err) throw err;
console.log("Connected!");
});
con.query('select * from accounts', function (err, rows, fields) {
if (err) throw err;
console.log(rows);
console.log('accountNumber is : ', rows[0].accountNumber);
result = rows[0].accountNumber;
});
console.log('result is : ', result);
var response = result;
return {
headers: {
'Content-Type': 'application/xml',
'Connection': 'Keep-Alive'
},
body: response
};
}
The result of the console log is:
result is :
Connected!
[ RowDataPacket { accountNumber: 777777, accountBalance: 777 } ]
accountNumber is : 777777
Not sure what I'm doing wrong and why the result is : lines comes up first despite being later in the code.
Any advice appreciated.
Full disclosure, I've been using mountebank for about two weeks so I'm a real beginner.
The function keyword inside connect and query is called callbacks, and only executed after the function itself is done. so your code would look like:
con.connect(function(err) {
if (err) throw err;
console.log("Connected!");
con.query('select * from accounts', function (err, rows, fields) {
if (err) throw err;
console.log(rows);
console.log('accountNumber is : ', rows[0].accountNumber);
result = rows[0].accountNumber;
console.log('result is : ', result);
var response = result;
});
});
and so on, but you just introduced callback hell to your code.
async is your friend.
EDIT:
following an example:
async.waterfall([
function (callback) {
//do some async function here
con.connect(function(err) {
if (err) throw err;
console.log("Connected!");
//call this when you are done
//you can even pass param to next function
callback(null,true);
});
},function (isConnected,callback1) {
if !(isConnected){
console.log("Connection failed! Skipping Query...")
callback1(null,"Error");
}
//do another async function here:
con.query('select * from accounts', function (err, rows, fields) {
if (err) throw err;
console.log(rows);
console.log('accountNumber is : ', rows[0].accountNumber);
result = rows[0].accountNumber;
callback1(null,"Complete");
});
}
], function (err,result) {
if(result == "Error"){
alert("Someting went wrong!");
}
if(result == "Complete"){
alert("Done!");
}
return 0;
});
note:I haven't written JS for awhile. Written this off of some existing code and haven't been tested. Also, Promise is also something that would help, but haven't looked into personally. BlueBird is a library for that.
The simplest way to get Data form mysql database using Promise and async await.
Get data dynamically by providing id to the SQL query.
With the help of following code snippet. First Your query will get execute fully the other process will execute.
response will be sent after execution of query is fully done. (sometimes response is sent first then execution of query completes)
async function getData(customerId){
let sql = `SELECT * FROM customer_info WHERE customerID = ${customerId}`
await connection.query(sql, (err, result) => {
data = {
CustomerId : result[0].customerID,
FirstName: result[0].FirstName,
LastName: result[0].LastName
}
})
}
function connectToDB(customerId){
return new Promise((resolve, reject) => {
getData(customerId).then(()=>resolve())
})
}
app.get('/customer/:id', (req, res) => {
let customerId = req.params.id
// Caller Function to all functions
async function callerFun(){
await connectToDB(customerId);
res.send("Execution Done");
}
callerFun();
})
I have a python background and is currently migrating to node.js. I have problem adjusting to node.js due to its asynchronous nature.
For example, I am trying to return a value from a MySQL function.
function getLastRecord(name)
{
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
}
else {
//console.log(rows);
return rows;
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
}
var rows = getLastRecord('name_record');
console.log(rows);
After some reading up, I realize the above code cannot work and I need to return a promise due to node.js's asynchronous nature. I cannot write node.js code like python. How do I convert getLastRecord() to return a promise and how do I handle the returned value?
In fact, what I want to do is something like this;
if (getLastRecord() > 20)
{
console.log("action");
}
How can this be done in node.js in a readable way?
I would like to see how promises can be implemented in this case using bluebird.
This is gonna be a little scattered, forgive me.
First, assuming this code uses the mysql driver API correctly, here's one way you could wrap it to work with a native promise:
function getLastRecord(name)
{
return new Promise(function(resolve, reject) {
// The Promise constructor should catch any errors thrown on
// this tick. Alternately, try/catch and reject(err) on catch.
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
connection.query(query_str, query_var, function (err, rows, fields) {
// Call reject on error states,
// call resolve with results
if (err) {
return reject(err);
}
resolve(rows);
});
});
}
getLastRecord('name_record').then(function(rows) {
// now you have your rows, you can see if there are <20 of them
}).catch((err) => setImmediate(() => { throw err; })); // Throw async to escape the promise chain
So one thing: You still have callbacks. Callbacks are just functions that you hand to something to call at some point in the future with arguments of its choosing. So the function arguments in xs.map(fn), the (err, result) functions seen in node and the promise result and error handlers are all callbacks. This is somewhat confused by people referring to a specific kind of callback as "callbacks," the ones of (err, result) used in node core in what's called "continuation-passing style", sometimes called "nodebacks" by people that don't really like them.
For now, at least (async/await is coming eventually), you're pretty much stuck with callbacks, regardless of whether you adopt promises or not.
Also, I'll note that promises aren't immediately, obviously helpful here, as you still have a callback. Promises only really shine when you combine them with Promise.all and promise accumulators a la Array.prototype.reduce. But they do shine sometimes, and they are worth learning.
I have modified your code to use Q(NPM module) promises.
I Assumed your 'getLastRecord()' function that you specified in above snippet works correctly.
You can refer following link to get hold of Q module
Click here : Q documentation
var q = require('q');
function getLastRecord(name)
{
var deferred = q.defer(); // Use Q
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
deferred.reject(err);
}
else {
//console.log(rows);
deferred.resolve(rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
return deferred.promise;
}
// Call the method like this
getLastRecord('name_record')
.then(function(rows){
// This function get called, when success
console.log(rows);
},function(error){
// This function get called, when error
console.log(error);
});
I am new to Node.js and promises. I was searching for a while for something that will meet my needs and this is what I ended up using after combining several examples I found. I wanted the ability to acquire connection per query and release it right after the query finishes (querySql), or to get a connection from pool and use it within Promise.using scope, or release it whenever I would like it (getSqlConnection).
Using this method you can concat several queries one after another without nesting them.
db.js
var mysql = require('mysql');
var Promise = require("bluebird");
Promise.promisifyAll(mysql);
Promise.promisifyAll(require("mysql/lib/Connection").prototype);
Promise.promisifyAll(require("mysql/lib/Pool").prototype);
var pool = mysql.createPool({
host: 'my_aws_host',
port: '3306',
user: 'my_user',
password: 'my_password',
database: 'db_name'
});
function getSqlConnection() {
return pool.getConnectionAsync().disposer(function (connection) {
console.log("Releasing connection back to pool")
connection.release();
});
}
function querySql (query, params) {
return Promise.using(getSqlConnection(), function (connection) {
console.log("Got connection from pool");
if (typeof params !== 'undefined'){
return connection.queryAsync(query, params);
} else {
return connection.queryAsync(query);
}
});
};
module.exports = {
getSqlConnection : getSqlConnection,
querySql : querySql
};
usage_route.js
var express = require('express');
var router = express.Router();
var dateFormat = require('dateformat');
var db = require('../my_modules/db');
var getSqlConnection = db.getSqlConnection;
var querySql = db.querySql;
var Promise = require("bluebird");
function retrieveUser(token) {
var userQuery = "select id, email from users where token = ?";
return querySql(userQuery, [token])
.then(function(rows){
if (rows.length == 0) {
return Promise.reject("did not find user");
}
var user = rows[0];
return user;
});
}
router.post('/', function (req, res, next) {
Promise.resolve().then(function () {
return retrieveUser(req.body.token);
})
.then(function (user){
email = user.email;
res.status(200).json({ "code": 0, "message": "success", "email": email});
})
.catch(function (err) {
console.error("got error: " + err);
if (err instanceof Error) {
res.status(400).send("General error");
} else {
res.status(200).json({ "code": 1000, "message": err });
}
});
});
module.exports = router;
I am still a bit new to node, so maybe I missed something let me know how it works out. Instead of triggering async node just forces it on you, so you have to think ahead and plan it.
const mysql = require('mysql');
const db = mysql.createConnection({
host: 'localhost',
user: 'user', password: 'password',
database: 'database',
});
db.connect((err) => {
// you should probably add reject instead of throwing error
// reject(new Error());
if(err){throw err;}
console.log('Mysql: Connected');
});
db.promise = (sql) => {
return new Promise((resolve, reject) => {
db.query(sql, (err, result) => {
if(err){reject(new Error());}
else{resolve(result);}
});
});
};
Here I am using the mysql module like normal, but instead I created a new function to handle the promise ahead of time, by adding it to the db const. (you see this as "connection" in a lot of node examples.
Now lets call a mysql query using the promise.
db.promise("SELECT * FROM users WHERE username='john doe' LIMIT 1;")
.then((result)=>{
console.log(result);
}).catch((err)=>{
console.log(err);
});
What I have found this useful for is when you need to do a second query based on the first query.
db.promise("SELECT * FROM users WHERE username='john doe' LIMIT 1;")
.then((result)=>{
console.log(result);
var sql = "SELECT * FROM friends WHERE username='";
sql = result[0];
sql = "';"
return db.promise(sql);
}).then((result)=>{
console.log(result);
}).catch((err)=>{
console.log(err);
});
You should actually use the mysql variables, but this should at least give you an example of using promises with mysql module.
Also with above you can still continue to use the db.query the normal way anytime within these promises, they just work like normal.
Hope this helps with the triangle of death.
You don't need to use promises, you can use a callback function, something like that:
function getLastRecord(name, next)
{
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
next(err);
}
else {
//console.log(rows);
next(null, rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
}
getLastRecord('name_record', function(err, data) {
if(err) {
// handle the error
} else {
// handle your data
}
});
Using the package promise-mysql the logic would be to chain promises using then(function(response){your code})
and
catch(function(response){your code}) to catch errors from the "then" blocks preceeding the catch block.
Following this logic, you will pass query results in objects or arrays using return at the end of the block. The return will help passing the query results to the next block. Then, the result will be found in the function argument (here it is test1). Using this logic you can chain several MySql queries and the code that is required to manipulate the result and do whatever you want.
the Connection object is created to be global because every object and variable created in every block are only local. Don't forget that you can chain more "then" blocks.
var config = {
host : 'host',
user : 'user',
password : 'pass',
database : 'database',
};
var mysql = require('promise-mysql');
var connection;
let thename =""; // which can also be an argument if you embed this code in a function
mysql.createConnection(config
).then(function(conn){
connection = conn;
let test = connection.query('select name from records WHERE name=? LIMIT 1',[thename]);
return test;
}).then(function(test1){
console.log("test1"+JSON.stringify(test1)); // result of previous block
var result = connection.query('select * from users'); // A second query if you want
connection.end();
connection = {};
return result;
}).catch(function(error){
if (connection && connection.end) connection.end();
//logs out the error from the previous block (if there is any issue add a second catch behind this one)
console.log(error);
});
To answer your initial question: How can this be done in node.js in a readable way?
There is a library called co, which gives you the possibility to write async code in a synchronous workflow. Just have a look and npm install co.
The problem you face very often with that approach, is, that you do not get Promise back from all the libraries you like to use. So you have either wrap it yourself (see answer from #Joshua Holbrook) or look for a wrapper (for example: npm install mysql-promise)
(Btw: its on the roadmap for ES7 to have native support for this type of workflow with the keywords async await, but its not yet in node: node feature list.)
This can be achieved quite simply, for example with bluebird, as you asked:
var Promise = require('bluebird');
function getLastRecord(name)
{
return new Promise(function(resolve, reject){
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
reject(err);
}
else {
resolve(rows);
//console.log(rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
});
}
getLastRecord('name_record')
.then(function(rows){
if (rows > 20) {
console.log("action");
}
})
.error(function(e){console.log("Error handler " + e)})
.catch(function(e){console.log("Catch handler " + e)});
May be helpful for others, extending #Dillon Burnett answer
Using async/await and params
db.promise = (sql, params) => {
return new Promise((resolve, reject) => {
db.query(sql,params, (err, result) => {
if(err){reject(new Error());}
else{resolve(result);}
});
});
};
module.exports = db;
async connection(){
const result = await db.promise("SELECT * FROM users WHERE username=?",[username]);
return result;
}
I am trying following code at node js using mysql but getting error "Cannot enqueue Query after invoking quit.
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'USER',
password : 'PASS',
database : 'DB',
});
connection.connect();
var queryString = 'SELECT * FROM tbl_product';
connection.query(queryString, function(err, rows, fields) {
if (err) throw err;
for (var i in rows) {
console.log('Product Name: ', rows[i].product_name);
var emp_query = 'SELECT * FROM tbl_employer';
connection.query(queryString, function(emp_err, emp_rows, emp_fields) {
if (emp_err) throw emp_err;
for (var e in emp_rows) {
console.log('Employer Name: ', emp_rows[e].company_name);
}
});
}
});
connection.end();
I see two problems in your code:
You're calling connection.end() synchronously, but your queries run in a asynchronous flow. You have to call connection.end() only when you've finished the second query.
You're using a regular for loop to run assynchronous calls (you outter loop).
To accomplish what you're trying to do, you have to consider those assynchronous scenarios. You could use promises or a module like async, that provides you a lot of methods to deal with assyncronous flows, like async.each():
connection.query(queryString, function(err, rows, fields) {
if (err) throw err;
async.each(rows, function (row, callback) {
console.log('Product Name: ', row.product_name);
var emp_query = 'SELECT * FROM tbl_employer';
connection.query(queryString, function(emp_err, emp_rows, emp_fields) {
if (emp_err) callback(emp_err);
for (var e in emp_rows) {
console.log('Employer Name: ', emp_rows[e].company_name);
}
callback();
});
});
}, function (err) {
connection.end();
}
});
Now it will guarantee that connection.end() will just be called when all your queries have finished.
Remove connection end function
==> connection.end();
The problem is connection.end() triggered before your query is not finished yet. Try to put connection.end() to end of outer loop.
connection.query(queryString, function(err, rows, fields) {
if (err) throw err;
for (var i in rows) {
console.log('Product Name: ', rows[i].product_name);
var emp_query = 'SELECT * FROM tbl_employer';
connection.query(queryString, function(emp_err, emp_rows, emp_fields) {
if (emp_err) throw emp_err;
for (var e in emp_rows) {
console.log('Employer Name: ', emp_rows[e].company_name);
}
});
}
connection.end();
});
Hope it will be useful for you.
I have the following function that gets a hexcode from the database
function getColour(username, roomCount)
{
connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
{
if (err) throw err;
return result[0].hexcode;
});
}
My problem is that I am returning the result in the callback function but the getColour function doesn't return anything. I want the getColour function to return the value of result[0].hexcode.
At the moment when I called getColour it doesn't return anything
I've tried doing something like
function getColour(username, roomCount)
{
var colour = '';
connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
{
if (err) throw err;
colour = result[0].hexcode;
});
return colour;
}
but of course the SELECT query has finished by the time return the value in colour
You have to do the processing on the results from the db query on a callback only. Just like.
function getColour(username, roomCount, callback)
{
connection.query('SELECT hexcode FROM colours WHERE precedence = ?', [roomCount], function(err, result)
{
if (err)
callback(err,null);
else
callback(null,result[0].hexcode);
});
}
//call Fn for db query with callback
getColour("yourname",4, function(err,data){
if (err) {
// error handling code goes here
console.log("ERROR : ",err);
} else {
// code to execute on data retrieval
console.log("result from db is : ",data);
}
});
If you want to use promises to avoid the so-called "callback hell" there are various approaches.
Here's an example using native promises and the standard MySQL package.
const mysql = require("mysql");
//left here for testing purposes, although there is only one colour in DB
const connection = mysql.createConnection({
host: "remotemysql.com",
user: "aKlLAqAfXH",
password: "PZKuFVGRQD",
database: "aKlLAqAfXH"
});
(async () => {
connection.connect();
const result = await getColour("username", 2);
console.log(result);
connection.end();
})();
function getColour(username, roomCount) {
return new Promise((resolve, reject) => {
connection.query(
"SELECT hexcode FROM colours WHERE precedence = ?",
[roomCount],
(err, result) => {
return err ? reject(err) : resolve(result[0].hexcode);
}
);
});
}
In async functions, you are able to use the await expression which will pause the function execution until a Promise is resolved or rejected. This way the getColour function will return a promise with the MySQL query which will pause the main function execution until the result is returned or a query error is thrown.
A similar but maybe more flexible approach might be using a promise wrapper package of the MySQL library or even a promise-based ORM.