NodeJS: How to stop code execution till create operation to MySQL completes - mysql

Question

I have a very basic scenario, I am making a create operation call to MySQL in my NodeJS application. Once I get result of create operation (success or failure) I have to execute some code.
But now due to asynchronous behavior of NodeJS my code which is dependent on result MySQL create operation is getting executed before MySQL create operation sends results back.
Here is my code
calculation.js
var mysql = require("mysql");
var methods = {};
// Creating connection
methods.executeQuery = function(selectQuery, values){
var result;
var con = mysql.createConnection({
host: "localhost",
user: "root",
password: "*********",
database: "******"
});
// getting connection
con.connect(function(err){
if(err){
console.log('Error connecting to Db');
return;
}
console.log('Connection established');
});
con.query(selectQuery, values, function(err,rows){
if(err) throw err;
console.log(rows);
result = rows;
console.log(result);
return result;
});
}
module.exports = methods;
client.js
var execute = require("./calculate.js");
var selectQuery = 'INSERT INTO users (username,password) VALUES (?,?)';
var values = ['sohamsoham12','sohamsoham12'];
var insertedRowInfo = execute.executeQuery(selectQuery, values);
if(insertedRowInfo){
console.log("true");
}else{
console.log("false");
}

Answer 1

I don't know if I correctly understand your question (what is the "create operation", for example?). But...
You can try this solution: execute the query inside the connect success callback:
// getting connection and executing query
con.connect(function(err){
if(err){
console.log('Error connecting to Db');
return;
}
console.log('Connection established');
con.query(selectQuery, values, function(err,rows){
if(err) throw err;
console.log(rows);
result = rows;
console.log(result);
return result; // this can't work... you should invoke a callback function, here...
});
});
UPDATE:
After OP comment, I now fully understand the question... (sorry :-().
You just miss a bit of async behavior... :-)
You should simply change methods.executeQuery from
function(selectQuery, values) {
...
}
to
function(selectQuery, values, callback) {
...
}
Then, instead using
return result;
You should simply use
callback(err, result); // if any error occurred
or
callback(null, result); // if no error occurred
Then, in client.js, when calling the executeQuery method, instead of
var insertedRowInfo = execute.executeQuery(selectQuery, values);
You should simply do
execute.executeQuery(selectQuery, values, function(err, insertedRowInfo) {
if (err) {
// handle error
} else {
// handle success, using insertedRowInfo...
}
});