Getting familiar with OOP - Factories

Question

I have no idea if I'm doing this efficiently, or ideally, but I've written what I think is a factory. Please help me understand if this is good practice, or if there is another direction I should take this. There's no particular project in mind with this, I'm just farting around. (Written in PHP)

class Factory
{
 private function __construct(){}
/**
 * @param $obj Object to Create.
 * @param $params Params (use array for multiple parameters) to be passed.
 */
 public static function build($obj, $params=null) {
 switch ($obj) {
 case 'db': return new DB($params);
 default: return null;
 }
 }
}

This lets me do something like $db = Factory::build("db","test_database_name"); The DB class just builds a PDO connection using appropriate parameters based on the database I'm trying to access, which is useful for me because I deal with MySQL and MS SQL all day long, and I don't want to have to remember all the connection strings, users, and passwords (stored in the DB class). That's kind of besides the point, I just intend this to be expanded as I develop more useful classes, so...

I just want to get some opinions on the the topic of a Factory. Is this a good method? are there others that are considered superior? If so, what have I overlooked?

• jdstankosky: Is Wouter J the only one with any input on this?

Answer 1

In my opinion, a factory should create a specific class, global ones like this one shouldn't be used. For instance, having a PizzaFactory is something like this:

class PizzaFactory
{
 public static function createPizza($type)
 {
 switch ($type) {
 case 'salami':
 return new SalamiPizza();
 break;
 case 'hawai':
 return new HawaiPizza();
 break;
 }
 }
}

I just want to get some opinions on the the topic of a Factory. Is this a good method? are there others that are considered superior? If so, what have I overlooked?

An upcomming design pattern is depedency-injection. Just search for some resoures about that and keep reading. It is used in all modern frameworks (ZF2 and Symfony 2 uses it).

See also this article serie by Fabien Potencier: "What is Dependency Injection?"

• jdstankosky: I'd actually agree with the factories building a specific type of thing. The DB class was the only one I had written thus far, although I could use it directly as $db = new DB("db_name"); to connect to any of my many databases... This Dependency Injection stuff kinda seems (at first glance) like regular factories (as I envision them), but backwards. All it is, is passing objects as parameters into other objects?