How can I use “Dependency Injection” in simple php functions, and should I bother?

by

Dependency injection is a big word for “I have some more parameters in my constructor”.

It’s what you did before the awfull Singleton wave when you did not like globals :

<?php
class User {
    private $_db;
    function __construct($db) {
        $this->_db = $db;
    }
}

$db   = new Db();
$user = new User($db);

Now, the trick is to use a single class to manage your dependencies, something like that :

class DependencyContainer 
{
    private _instances = array();
    private _params = array();

    public function __construct($params)
    {
        $this->_params = $params;
    }

    public function getDb()
    {
        if (empty($this->_instances['db']) 
            || !is_a($this->_instances['db'], 'PDO')
        ) {
            $this->_instances['db'] = new PDO(
                $this->_params['dsn'],
                $this->_params['dbUser'], 
                $this->_params['dbPwd']
            );
        }
        return $this->_instances['db'];
    }
}

class User
{
    private $_db;
    public function __construct(DependencyContainer $di)
    {
         $this->_db = $di->getDb();
    }
}

$dependencies = new DependencyContainer($someParams);
$user = new User($dependencies);

You must think you just another class and more complexity. But, your user class may need something to log messages like lot of other classes. Just add a getMessageHandler function to your dependency container, and some $this->_messages = $di->getMessageHandler() to your user class. Nothing to change in the rest of your code.

You’ll get lot of infos on symfony’s doc

More Related Contents:

  1. Dependency Hell — how does one pass dependencies to deeply nested objects?
  2. Understanding IoC Containers and Dependency Injection
  3. Symfony 2 EntityManager injection in service
  4. Pass array literal to PostgreSQL function
  5. How to inject a repository into a service in Symfony?
  6. PHP Function with Optional Parameters [duplicate]
  7. Unresolvable dependency resolving [Parameter #0 [ $name ]]
  8. How to pass parameters from bash to php script?
  9. How to pass variables between php scripts?
  10. PHP, pass parameters from command line to a PHP script
  11. URL Redirect / URL Masking [closed]
  12. Get the full URL in PHP
  13. Replace the Variable Price range by the chosen variation price in WooCommerce 3
  14. Is there a PHP Sandbox, something like JSFiddle is to JS? [closed]
  15. mysqli ignoring the first row in a table
  16. PHP Create and Save a txt file to root directory
  17. Artisan migrate could not find driver
  18. How to check if $_GET is empty?
  19. another twitter oAuth cURL access token request that fails
  20. Absolute vs. relative paths
  21. PHP object like array
  22. What is the best way to insert multiple rows in PHP PDO MYSQL?
  23. Why doesn’t PHP print TRUE/FALSE? [duplicate]
  24. Move an array element to a new index in PHP
  25. Reference Guide: What does this symbol mean in PHP? (PHP Syntax)
  26. Detecting file upload size on the client side?
  27. Validate Email in php [duplicate]
  28. saving checkbox state on reload
  29. Update Command-line Output, i.e. for Progress
  30. Laravel Eloquent update just if changes have been made

Leave a Comment