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How to check if the db connection is success or not in node js and mysql

I'm using mysql connection pool to create connection. The code looks like the following.
var pool = mysql.createPool(connectionProps);
by accessing pool, I'll get the an Object, even if the connection is not Successful. I checked it with starting and stopping mysql.
What I want is that, I need to check connection is successful or not as follows.
if(pool){ // mysql is started && connected successfully.
console.log('Connection Success');
doSomething();
}else{
console.log('Cant connect to db, Check ur db connection');
}
I want something like this. So how can we do this with the mysql pool Object. Can someone please help me?
Thanks n Regards

Commonly you would do something like select something arbitrary from the db, and catch an error if that failed. Example from the docs.
const pool = mysql.createPool(connectionProps);
pool.query('SELECT 1 + 1 AS solution', (error, results, fields) => {
if (error) throw error;
console.log('The solution is: ', results[0].solution);
});

var pool = mysql.createPool(config.db);
exports.connection = {
query: function () {
var queryArgs = Array.prototype.slice.call(arguments),
events = [],
eventNameIndex = {};
pool.getConnection(function (err, conn) {
if (err) {
if (eventNameIndex.error) {
eventNameIndex.error();
}
}
if (conn) {
var q = conn.query.apply(conn, queryArgs);
q.on('end', function () {
conn.release();
});
events.forEach(function (args) {
q.on.apply(q, args);
});
}
});
return {
on: function (eventName, callback) {
events.push(Array.prototype.slice.call(arguments));
eventNameIndex[eventName] = callback;
return this;
}
};
}
};
And require to use it like:
db.connection.query("SELECT * FROM `table` WHERE `id` = ? ", row_id)
.on('result', function (row) {
setData(row);
})
.on('error', function (err) {
callback({error: true, err: err});
});

Async.waterfall function gets called twice

I have an async waterfall Array where the function otherIngrLists() is the 3rd to be executed. Every function before that worked fine.
function otherIngrLists(userslist, callback){
collection = db.get('ingrList');
collection.find({"userid":{$ne:userid}},{},function(err,docs){
if(!err){
var otherLists = docs;
var otherListsCount = docs.count();
console.log(otherListsCount);
callback(null, otherLists, otherListsCount, userslist);
} else {
callback(err, null);
}
});
},
The Problem is that this function is called twice. I assured this with a simple console.log().
How did I manage to call this function again? Did I get the concept of callbacks wrong as I use them to be passed on to the next function?
Also after this function executing twice an error ist thrown. It has nothing to to with this problem though and I will concern my self with that later.
Thank you for your time!
Waterfall Array in router.get:
router.get('/:userid', function(req, res) {
var db = req.db;
var collection;
var userid = req.params.userid;
async.waterfall(
[
function getIngrList(callback, userid) {
var route = 'http://localhost:3000/users/zutatenliste/'+userid;
request(route, function(err, response, body){
if (!err && response.statusCode === 200) {
var userlist = body;
callback(null, userlist);
} else {
callback(err, null);
return;
}
});
},
function otherIngrLists(userlist, callback){
collection = db.get('zutatenListe');
console.log(userid);
collection.find({"userid":{$ne:userid}},{},function(err,docs){
if(!err){
var otherLists = docs;
var otherListsCount = docs.count();
callback(null, otherLists, otherListsCount, userlist);
} else {
callback(err, null);
}
});
},
function pushInArray(otherLists, otherListsCount, userlist, callback){
console.log("test");
...
...}
}
}
Edit 1: --Also either if cases are executed, first the true one then the false--
// Does not happen anymore
Edit 2: Added the whole Thing until the problematic function

Please provide some Additional details as this function seems perfect and No, You haven't misunderstood the concept of callback you are using it correctly.
Structure of Async Waterfall
var create = function (req, res) {
async.waterfall([
_function1(req),
_function2,
_function3
], function (error, success) {
if (error) { alert('Something is wrong!'); }
return alert('Done!');
});
};
function _function1 (req) {
return function (callback) {
var something = req.body;
callback (null, something);
}
}
function _function2 (something, callback) {
return function (callback) {
var somethingelse = function () { // do something here };
callback (err, somethingelse);
}
}
function _function3 (something, callback) {
return function (callback) {
var somethingmore = function () { // do something here };
callback (err, somethingmore);
}
}
so, in waterfall you can pass the values to the next function and your 3rd function is correct.
Edited
async.waterfall(
[
//can not give userId as second parameter
function getIngrList(callback) {
//if you want userId you can pass as I shown above or directly use here if it's accessible
var route = 'http://localhost:3000/users/zutatenliste/'+userid;
request(route, function(err, response, body){
if (!err && response.statusCode === 200) {
var userlist = body;
callback(null, userlist);
} else {
callback(err, null);
// return; no need
}
});
},
function otherIngrLists(userlist, callback){
collection = db.get('zutatenListe');
console.log(userid);
collection.find({"userid":{$ne:userid}},{},function(err,docs){
if(!err){
var otherLists = docs;
var otherListsCount = docs.count();
callback(null, otherLists, otherListsCount, userlist);
} else {
callback(err, null);
}
});
},
function pushInArray(otherLists, otherListsCount, userlist, callback){
console.log("test");
...
...}
As said you can not pass userId as last parameter over there. Let me know if you still get the same error.

First you need to declare you function:
function myFuntion(userId, callback) {
async.waterfall([
function(callback) {
//do some thing here
callback(null, userlist);
}, function(userId, callback) {
//do something here
callback(null, orderList, orderListCount, userlist);
}
], function(err, orderList, orderListCount, userlist) {
if(err)
console.log(err);
else
callback(orderList, orderList, userlist);
})
}
After that you can use function:
myFuntion(userId, function(orderList, orderListCount, userlist) {
console.log(orderList);
console.log(orderListCount);
console.log(userlist);
})

Getting error can not get header after they send when read files from directory?

I am trying to get the name and created date of the files. In the code below it throws error when I call the api. It is reading the directory and printing all the file names but it's not sending back to callback. Any idea what is implemented wrong?
service.js
var fs = require('fs');
var path = require('path');
var async = require('async');
var currentDate = new Date();
var objToReturn = [];
var logsDirectory = './logs'
function readDirectory(env, callback) {
fs.readdir(logsDirectory + '/' + env, function(err, files) {
// loop through each file
async.eachSeries(files, function(file, done) {
var dirPath = logsDirectory + '/' + env;
var filePath = path.join(dirPath, file);
var fileInfo = {};
fs.stat(filePath, function(err, stats) {
if (err) {
console.info("File doesn't exist");
} else {
fileInfo.fileDate = stats.birthtime;
fileInfo.filename = file;
objToReturn.push(fileInfo);
done();
}
});
});
},
function(err) {
if (err) {
console.info('error', err);
return;
}
// when you're done reading all the files, do something...
console.log('before Callback', objToReturn);
callback(objToReturn);
});
}
exports.readDirectory = readDirectory;
app.js
var stDirectory = require('./app/serverfiles/stDir');
app.get('/getAllFiles',function(req,res){
var env = req.query.env
console.log('printing',env);
stDirectory.readDirectory(env,function(files){
res.json(files);
console.log('Api files',files);
});
});

There are a few issues:
instead of passing the "final" handler to async.eachSeries(), you're passing it to fs.readdir(), so callback will never get called;
you're declaring objToReturn outside of the function, which isn't a good idea because multiple requests could be handled in parallel;
you're not handling any errors properly;
you should really use the Node.js callback idiom of calling callbacks with two arguments, the first being errors (if there are any) and the second being the result of the asynchronous operation.
The code below should fix these issues:
function readDirectory(env, callback) {
let objToReturn = [];
fs.readdir(
logsDirectory + "/" + env,
function(err, files) {
if (err) return callback(err);
// loop through each file
async.eachSeries(files, function(file, done) {
var dirPath = logsDirectory + "/" + env;
var filePath = path.join(dirPath, file);
var fileInfo = {};
fs.stat(filePath, function(err, stats) {
if (err) {
console.info("File doesn't exist");
return done(err);
} else {
fileInfo.fileDate = stats.birthtime;
fileInfo.filename = file;
objToReturn.push(fileInfo);
done();
}
});
}, function(err) {
if (err) {
console.info("error", err);
return callback(err);
}
// when you're done reading all the files, do something...
console.log("before Callback", objToReturn);
callback(null, objToReturn);
}
);
}
// To call it:
stDirectory.readDirectory(env, function(err, files) {
if (err) {
res.sendStatus(500);
} else {
res.json(files);
console.log('Api files',files);
}
});
You should also consider using async.mapSeries() instead of async.eachSeries() and using a separate array (objToReturn).

howto Node module.exports

I want to separate the code for executing mysql query in Node, so I am trying to use the Revealing Module pattern here
/* pool -create connection pool mysql*/
var sqlQuery = function (sqlString) {
var _result = pool.getConnection(function (err, connection) {
/* error handling*/
connection.query(sqlString, function (err, rows) {
console.log(this.sql);
if (!err) {
return _result = rows; <============
}
connection.release();
});
return;
});
console.log(_result);
return { recordSet : _result }
};
module.exports = sqlQuery;
How can I return rows to my app.js. the code below for calling sqlQuery is not working
var SqlQuery = require(./path/to/sqlQueryFile);
var rows = SqlQuery('pass sql here').recordSet;
console.log(row);
res.json(rows);

Your code is asynchronous, but you're calling it synchronously.
If you wanted to do it like this, you'll also need to pass a callback to SqlQuery.
/* pool -create connection pool mysql*/
var sqlQuery = function (sqlString, callback) {
var _result = pool.getConnection(function (err, connection) {
/* error handling*/
connection.query(sqlString, function (err, rows) {
console.log(this.sql);
if (!err) {
callback(rows);
}
connection.release();
});
});
};
module.exports = sqlQuery;
And then call it with:
var SqlQuery = require(./path/to/sqlQueryFile);
var rows = SqlQuery('pass sql here', function(recordSet){
console.log(recordSet);
res.json(recordSet);
});
Edit: If you're using newer versions of JavaScript, you have a few more options.
If you have access to Promises, you can do this:
function sqlQuery (sqlString) {
return new Promise((resolve, reject) => {
pool.getConnection(function (err, connection) {
if (err) { return reject(err); } // error handling
connection.query(sqlString, function (err, rows) {
if (err) { return reject(err); }
resolve(rows);
connection.release();
});
});
});
}
module.exports = sqlQuery;
And then you'd use it like:
var SqlQuery = require(./path/to/sqlQueryFile);
SqlQuery('pass sql here')
.then(function(recordSet) {
console.log(recordSet);
res.json(recordSet);
})
.catch(function(err) {
// do your error handling
res.status(500).json({ err: 'Sorry there was an error' });
});
If you're using even newer JavaScript, you can use the async/await syntax (currently available via Babel, and I think in FireFox. Chrome in V55).
var SqlQuery = require(./path/to/sqlQueryFile);
async handleQuery(query) {
try {
var rows = await SqlQuery(query);
res.json(rows);
} catch (e) {
console.log('Error!', e);
}
}
To chain multiple queries together:
async handleQuery(query) {
try {
return await SqlQuery(query);
} catch (e) {
console.log('Error!', e);
}
}
var rows = await handleQuery('select * from tablename');
var rowsToReturn = await handleQuery('select id from another_table where name = "' + rows[0].name + '"');

How to invoke a function in Meteor.methods and return the value

Can you please tell me how I can invoke a function when I make a meteor method/call.
For test purposes and keeping it simple, I get a value of 'undefined' on the client console.
Server.js
Meteor.methods({
testingFunction: function() {
test()
}
});
function test(){
var name = 'test complete'
return name
}
client.js
Template.profile.events({
'click #button': function (event) {
event.preventDefault();
Meteor.call('testingFunction', function(error, response) {
if (error) {
console.log(error);
} else {
console.log(response);
}
});
}
});

Any function without a return statement will return undefined. In this case, you need to add return test() to return the value of the call to test from your method.
Meteor.methods({
testingFunction: function() {
return test();
}
});

Here is a great example:
Client Side:
// this could be called from any where on the client side
Meteor.call('myServerMethod', myVar, function (error, result) {
console.log("myServerMethod callback...");
console.log("error: ", error);
console.log("result: ", result);
if(error){
alert(error);
}
if(result){
// do something
}
});
Server Side:
// use Futures for threaded callbacks
Future = Npm.require('fibers/future');
Meteor.methods({
myServerMethod: function(myVar){
console.log("myServerMethod called...");
console.log("myVar: " + myVar);
// new future
var future = new Future();
// this example calls a remote API and returns
// the response using the Future created above
var url = process.env.SERVICE_URL + "/some_path";
console.log("url: " + url);
HTTP.get(url, {//other params as a hash},
function (error, result) {
// console.log("error: ", error);
// console.log("result: ", result);
if (!error) {
future.return(result);
} else {
future.return(error);
}
}
);
return future.wait();
}//,
// other server methods
});