To retrieve a result set, we have to initialize a Criteria object and customize it. This object then represents an SQL query. As our custom classes extend the base class, we use one of a number of methods of the parent. Passing the Criteria object to the method results in the query that is performed on our database. The Criteria object can handle both simple and relatively complicated queries. However, as a rule it is a good practice to customize the Criteria object to only retrieve what you want. This will be covered in detail in Chapter 9,Optimizing for performance.

Opening the lib/model/MilkShakePeer.php file reveals that there are no methods. As this is a custom class, it is up to us to add our business logic. Here we need to create a static method to retrieve data about all the milkshakes from the database in alphabetical order. Let's begin by adding a getAllShakes() method, which I have done in the following code snippet:

/**
* Get all of the milkshakes
*
* @param Int $limit total amount to be returned. 0 = unlimited
* @return Array Array containing objects
*/
public static function getAllShakes($limit=0)
{
//Create the criteria
$c = new Criteria();
//Set the limit
if(0 > $limit)
{
$c->setLimit($limit);
}
//Order by name in ascending order
$c->addAscendingOrderByColumn(self::NAME);
return self::doSelect($c);
}

In this code snippet, we first instantiate the Criteria object and then customize the criteria by setting a limit, if one is required, using the setLimit() method. This translates into the SQL Limit clause. To set an order by clause, we need to use the Criteria object's addAscendingOrderByColumn() method. This method takes the column name with which we want to order the result set as an argument. That's all we need to do to the Criteria object. Next, we call the doSelect()parent method and pass it to our Criteria object.

The doSelect() method does more than just querying the database. After this function has been called, the results are returned to the method and then the results are converted into our model objects. The whole process is called hydration. Essentially, the following happens in the hydrating process:

This is a very quick and convenient way of retrieving our data. However, with ease comes danger. It is very easy to fall into the habit of retrieving everything even if we only need one or two columns. We'll look at bypassing the hydration process in Chapter 9,Optimizing for Performance.