Easy way to pass DB object into class that is extended numerous times

Question

Consider the following PHP code:

<?php
require_once("myDBclass.php");
class a {
    private $tablename;
    private $column;
    function __construct($tableName, $column) {
        $this->tableName = $tablename;
        $this->column = $column;        
    }

    function insert() {
        global $db;
        $db->query("INSERT INTO ".$this->tableName." (".$this->column.") VALUES (1)");  
    }       
}

class x extends a {
    function __construct() {
        parent::construct("x", "colX"); 
    }
}

class y extends a {
    function __construct() {
        parent::construct("y", "colY"); 
    }
}
?>

I have my $db object that is instantiated in another file but wish to somehow pass this into class a's functions without using the global keyword everytime i define a new function in class "a".

I know i can do this by passing the DB object when instantiating class X and Y, then passing it through to class A that way (like im currently doing with the tablename and column), however i never know how many times i might extend class A and thought that there must be another easier way somehow.

Does anybody know of a better solution that i could consider to achieve this?

Thanks in advance

Answer 1

Look into the Singleton Design Pattern. You should not have the need to use globals, as you seem to know it is not necessary.

Answer 2

You could use PHP's static properties.

class A {
    static $db;
    public static function setDB($db) {
        self::$db = $db;
    }
}

Now that property will be shared across all instances of that object and it's children.