I'm trying to work with MySQL in NodeJS. My entire app is built with promises, so I want to promisify the mysql module as well.

So I have this:

Promise = require('bluebird');
var mysql = Promise.promisifyAll(require('mysql'));

Now, according to their API, the connect() method accepts a single parameter, an err callback to be called in case of connection error. My question is, how does that translate to promises?

Will the promise be resolved on error? Will it be rejected? Will I need to .catch() it perhaps? How does that work?

I'm trying to work with MySQL in NodeJS. My entire app is built with promises, so I want to promisify the mysql module as well.

So I have this:

Promise = require('bluebird');
var mysql = Promise.promisifyAll(require('mysql'));

Now, according to their API, the connect() method accepts a single parameter, an err callback to be called in case of connection error. My question is, how does that translate to promises?

Will the promise be resolved on error? Will it be rejected? Will I need to .catch() it perhaps? How does that work?

• javascript
• mysql
• node.js
• promise
• bluebird

Share Improve this question Follow edited Dec 25, 2014 at 11:34 Benjamin Gruenbaum 277k8989 gold badges519519 silver badges514514 bronze badges asked Jul 17, 2014 at 7:25 Madara's GhostMadara's Ghost 175k5050 gold badges272272 silver badges314314 bronze badges

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1 Answer 1

Sorted by: Reset to default 8

If a method is a node "errback" with a single argument - it will be resolved with no parameters in the then or alternatively be rejected with the err passed to it. In the case of promisification, you can catch it with .error or use a catch with Promise.OperationalError.

Here is a simple approach:

function getConnection(){
    var connection = mysql.createConnection({
      host     : 'localhost',
      user     : 'me',
      password : 'secret'
    });
    return connection.connectAsync().return(connection); // <- note the second return
}

getConnection().then(function(db){
    return db.queryAsync(....);
}).error(function(){
   // could not connect, or query error
});

If this is for managing connections - I'd use Promise.using - here is a sample from the API:

var mysql = require("mysql");
// unment if necessary
// var Promise = require("bluebird");
// Promise.promisifyAll(mysql);
// Promise.promisifyAll(require("mysql/lib/Connection").prototype);
// Promise.promisifyAll(require("mysql/lib/Pool").prototype);
var pool  = mysql.createPool({
    connectionLimit: 10,
    host: 'example',
    user: 'bob',
    password: 'secret'
});

function getSqlConnection() {
    return pool.getConnectionAsync().disposer(function(connection) {
        try {
            connection.release();
        } catch(e) {};
    });
}

module.exports = getSqlConnection;

Which would let you do:

Promise.using(getSqlConnection(), function(conn){
    // handle connection here, return a promise here, when that promise resolves
    // the connection will be automatically returned to the pool.
});