Better PHP Development

Chapter 5: Disco with Design Patterns: A Fresh Look at Dependency Injection

by Reza Lavaryan

Dependency Injection is all about code reusability. It's a design pattern aiming to make high-level code reusable, by separating the object creation / configuration from usage.

Consider the following code:

<?php

class Test {

    protected $dbh;

    public function __construct(\PDO $dbh)
    {
        $this->dbh = $dbh;
    }

}

$dbh  = new PDO('mysql:host=localhost;dbname=test', 'username', 'password');
$test = new Test($dbh) 

As you can see, instead of creating the PDO object inside the class, we create it outside of the class and pass it in as a dependency - via the constructor method. This way, we can use the driver of our choice, instead of having to to use the driver defined ...