Building a bridge class that allows you to connect to MySQL by using either the traditional "mysql" library or the "mysqli" extension is a straightforward task that can be accomplished with minor effort.

In the prior section I defined a pair of MySQL wrapping classes aimed at accessing MySQL via a conventional approach. Therefor, the process for creating a bridge class is reduced to coding the mentioned class in such a way that it can be instructed programmatically of the type of interface to be used for accessing the database server.

Does this sound rather confusing to you? It really isn't, particularly if you take a look at the signature that corresponds to the class below:

// define 'BridgeMySQLConnector' class

class BridgeMySQLConnector{

	private $conInterface;

	private $db;
	
	public function __construct($host,$user,$password,$database,

$conInterface){
      
		if($conInterface!='mysql'&&$conInterface!='mysqli'){

			throw new Exception

('Invalid connection interface for MySQL');     
		}
      
		if($conInterface=='mysql'){

			$this->db=new MySQL($host,$user,$password,

$database);
		}

		else{

			$this->db=new mysqli($host,$user,$password,

$database);
		}

	}

	public function query($query){

		return $this->db->query($query);    
	}

} 

As you can see, the "BridgeMySQLConnector" class coded above accepts the typical set of parameters required for connecting to MySQL, that is the hostname, the user/password combination and the selected database, as well as the interface to be used for performing this process.

In addition, you should realize that the previous class strictly follows the model dictated by the bridge pattern. It will use the library passed in as a parameter for accessing the database server, but in all cases there's no specific implementation concerning how this task must be carried out.

Thus, what does all this mean? Yes, you guessed right! The logic required for connecting to MySQL has been completely decoupled from the class itself, since this procedure is tackled by the corresponding "bridged" objects, in this case referenced inside the class as "MySQL" and "mysqli" respectively. Building a bridge class with PHP 5 is actually easy after all, isn't it?

Well, now that you know how the prior "BridgeMySQLConnector" class works, it would be very instructive to develop a practical example where all the previous classes are used in conjunction. In this way, you'll see more clearly how this abstraction layer can be utilized for accessing the MySQL server.

As usual, if you want to learn how the layer in question will be put to work, go ahead and read the following section. I'll be there, waiting for you.