Adds aggregate .as() to define alias to previous function (#123)

Usually, when using .avg('age'), ORM will define an alias called
avg_age to the returned value. If you want to change this do
.avg('age').as('my_age').

Author: dresende

lib/AggregateFunctions.js

@@ -43,6 +43,17 @@ function AggregateFunctions(opts) {
 			                                                 Array.prototype.slice.apply(arguments));
 			return this;
 		},
+		as: function (alias) {
+			if (aggregates.length === 0) {
+				throw new Error("No aggregate function defined yet");
+			}
+
+			var len = aggregates.length;
+
+			aggregates[len - 2][aggregates[len - 2].length - 1].alias = alias;
+
+			return this;
+		},
 		get: function (cb) {
 			if (typeof cb != "function") {
 				throw new Error("You must pass a callback to Model.aggregate().get()");

test/integration/test-aggregate-alias.js

@@ -0,0 +1,24 @@
+var common     = require('../common');
+var assert     = require('assert');
+
+common.createConnection(function (err, db) {
+	common.createModelTable('test_aggregate', db.driver.db, function () {
+		common.insertModelData('test_aggregate', db.driver.db, [
+			{ id : 1, name : 'test1' },
+			{ id : 2, name : 'test2' },
+			{ id : 3, name : 'test3' },
+			{ id : 4, name : 'test4' },
+			{ id : 5, name : 'test5' }
+		], function (err) {
+			if (err) throw err;
+
+			var TestModel = db.define('test_aggregate', common.getModelProperties());
+
+			TestModel.aggregate({ id: common.ORM.gt(2) }).count('id').as('alias').get(function (err, alias) {
+				assert.equal(err, null);
+				assert.equal(alias, 3);
+				db.close();
+			});
+		});
+	});
+});