Make synchronous MySQL queries in NodeJS - mysql

Question

I have been doing google searches for 5 days, I hope to find the solution ... I know that it does not work because it is asynchronous, but I need the program (it is a Discord bot) to respond with a data that I get from a DB. I have tried Promises and callbacks, but I do not know if it is because I am a novice with asynchronous, that nothing works for me.
const con = mysql.createConnection({
host: datos.host,
user: datos.user,
password: datos.password,
database: datos.database
});
function leerPromesa() {
var promise = new Promise(function (resolve, reject) {
con.query('SELECT * from ranking;', function (err, rows, fields) {
if (err) {
reject(err);
return
}
resolve(rows);
rows.forEach(element => console.log(element));
})
});
return promise;
};
var promesa = leerPromesa();
promesa.then(
function (rows) {
rows.forEach(element => msg.reply(element));
},
function (err) {
msg.reply(err);
}
);
con.end();
What the bot does is respond with blank text.

Answer 1

First, you're not really connecting to database.
If you refer to docs https://github.com/mysqljs/mysql:
var connection = mysql.createConnection({
host : 'localhost',
user : 'me',
password : 'secret',
database : 'my_db'
});
// then connect method
connection.connect();
So your code will never work..
Second, you are closing connection before any query execution:
con.end();
Correct is to close connection after leerPromesa function execution.
Finally, code could look something like this:
const con = mysql.createConnection({
host: datos.host,
user: datos.user,
password: datos.password,
database: datos.database
});
con.connect();
function leerPromesa() {
return new Promise(function(resolve, reject) {
con.query("SELECT * from ranking;", function(err, rows, fields) {
if (err) {
return reject(err);
}
return resolve(rows);
});
});
}
leerPromesa()
.then(
function(rows) {
rows.forEach(element => msg.reply(element));
},
function(err) {
msg.reply(err);
}
)
.finally(function() {
con.end();
});
I used finally method on Promise to close connection in every situation https://developer.mozilla.org/ru/docs/Web/JavaScript/Reference/Global_Objects/Promise/finally