Example use of databases with Promises

gistfile1.js

var Q = require('q');
var DB = require('db');

// These DB initializations would probably not be synchronous in a real 
// app. You could use Q.spread(), etc. See sample #2.

var db1 = DB.openSync("db1");
var db2 = DB.openSync("db2");
var db3 = DB.openSync("db3");

/** Sample implementation of db.queryRow(). Please note that it should 
 * be included in the db library. However I think implementing it here 
 * is a great example of using Promises.
 */
DB.prototype.queryRow = function(str, opts) {
	return this.query(str, opts).when(function(rows) {
		var row = rows.shift();
		if(!row) return new TypeError("No enough rows!");
		return row;
	};
};

/* Our sample #1. It's our own function that returns a promise. */
function sample() {
	var result1, result2;
	return db1.queryRow("SELECT FROM foo WHERE id = {id}", {'id':1}).when(function(row1) {
		result1 = row1;
		if(result1.title) return result1.title;
		return db2.queryRow("SELECT FROM bar WHERE foo = {foo}", {'foo':result1.id}).when(function(row2) {
			result2 = row2;
			return result2.title;
		});
	}).when(function(title) {
		if(result1) console.log("result1 = " + JSON.stringify(result1));
		if(result2) console.log("result2 = " + JSON.stringify(result2));
		return "Title was " + title;
	});
} // end of sample

// Code for sample 1
sample().when(function(title) {
	console.log("Title = " + title);
}).fail(function(err) {
	console.error("ERROR: " + err);
}).done();

/** Sample #2 performing multiple operations at the same time and 
 * collecting results from all of them into one single response.
 */
function sample2() {
	// db.queryRow is same as db.query but it does the results.shift() 
	// for us and verifies that it's not undefined.
	var a = db1.queryRow("SELECT COUNT(*) AS rows FROM foo");
	var b = db2.queryRow("SELECT COUNT(*) AS rows FROM bar");
	var c = db3.queryRow("SELECT COUNT(*) AS rows FROM world");
	return Q.spread([a, b, c], function (a, b, c) {
		return a.rows + b.rows + c.rows;
	});
}

// Code for sample 2
sample2().when(function(rows) {
	console.log("Databases have total of " + rows + " rows.");
}).fail(function(err) {
	console.error("ERROR: " + err);
}).done();