Question

I’m creating a website with structure like this:

class main { }

class mysql extends main { }

class user extends main { }

class etc extends main { }

The idea is for these classes to use functions from each other. This doesn’t work. How can I call a function from mysql in user?

EDIT:
All errors are similar to this one:

Fatal error: Call to undefined method user::function_in_mysql() in C:\foo.php on line 8

Martti Laine

Answer 1

Having a class extend another makes the methods of the other (parent) available to it. So user extending main only makes the methods of main available to it. If other classes extend main it doesn’t allow all of them to call each others methods. You could have user extend mysql and mysql‘s methods would then be available to user though I don’t believe that fundamentally this is what you’re looking for.

I think you’re looking for something along the lines of dependency injection and not class inheritance.

For example if you wanted your user class to have access to your mysql class you pass it an instance of it in it’s constructor.

class user {
    protected $_mysql;

    public function __construct(mysql $mysql) {
        $this->_mysql = $mysql;
    }

    public function myMethod() {
        $this->_mysql->myMysqlMethod();
    }
}

$mysql = new mysql();
$user = new user($mysql);

$user->myMethod();

Here’s some good reading on dependency injection.

• PHP Dependency Injection
• Symphony Dependency Injection

The Symphony link in particular is a pretty nice read on the overview of dependency injection and how to setup a dependency container.