Pool Connection doubt.

[Luigi Padovani]

Hi People,

i using this function to get a generic Param from DB

function getData(param)

{

var queryString = 'SELECT value FROM data where config like "%'+param+'%"';

  pool.getConnection(function(err, connection){

if (err) {

    console.log(err);

    throw err;

   }

  connection.query(queryString, function(err, rows, fields) {

   if (err) {

    console.log(err);

    throw err;

   }

return rows[0].value;

 });

});

}

but when i use this function :

function setData()

{

timeoutEstrazione = getData('countdown')*1000;

timeoutBall = getData('balltime')*1000;

timeoutPause = getData('pausetime')*1000;

console.log('timeoutEstrazione:',timeoutEstrazione);

}

the console output timeoutEstrazione:NaN

the field was filled later, the Connection Pool was async respect the code flow.

anyone can suggest me the correct way to fix this problem?

thx a lot.

Luigi

[Ryan Lee]

You have flow control issues. Remember javascript is asynchronous. getData returns undefined before your mysql query completes.

You can either us the async library, or a promise library to help you do flow control. 

var async = require('async');

//common callback convention is too pass in parameters and a callback function

//callback function has the signuature (error, values)

//if error is set you need to handle it.

var getData = function (param, next) {

    //escape your query. You don't want a sql injection

    pool.query('SELECT value FROM data where config like %?%', param, function (err, rows) {

       //return here does nothing. It is to break execution if there is an error.

       if (err) { return next(err); }

       //process your data here or just return it.

       //notice the null means no error

       next(null, rows[0].value);

    });

};

//chose series, parallel, or waterfall depending on what you need to do

async.parallel([

  function (cb) {

    getData('countdown', function (err, data) {

       cb(err, data * 1000);

    });

  },

  function (cb) {

    getData('balltime', function (err, data) {

       cb(err, data * 1000);

    });

  },

  function (cb) {

    getData('pausetime', function (err, data) {

       cb(err, data * 1000);

    })

  }

], function (err, results) {

  if (err) { throw err; //handle error}

  //this is timeoutEstrazione.

  console.log(results[0]);

});

This is a quick and dirty example, but your issues come from flow control. Javascirpt does not return things the way you think it will.

Good luck.

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