Nodejs Mysql connection pooling using mysql module

Question

We are using mysql module for node and i was just wondering if this approach is good or does it have any bad effects on our application, consider this situation

dbPool.getConnection(function(err, db) {
    if(err) return err;
    db.query()

Here i am calling the dbPool object and requesting a connection from the pool then using it. However i found another implementation (which is the one i am asking about) which uses the dbPool object directly like:

dbPool.query('select * from test where id = 1' function(err, rows) {})

so i was wondering what does the second implementation does exactly, does it automatically return a free connection and use it ? can explain what is happening exactly in the second case and if it has any effect + or - on my application ? Thank you.

Answer 1

So this is so what called callback chaining. In NodeJS you have a lot of asynchronous calls going around. But sometimes you want to do something when the connection is done with MySQL. That's why the getConnection functionality has a callBack feature.

dbPool.getConnection(function(err, db) {
    if(err) return err;
    db.query()

Is equal to this:

dbPool.query('select * from test where id = 1' function(err, rows) {})

dbPool.query() will wait for the connection to be open, you don't have to put all your queries inside the getConnection to make it work. This is why it also has a callBack feature.

Tell me if I'm wrong. I hope this solves your question.