Question

Essentially, I am just creating two classes where one class, in this case class A, runs a function in another class, in this case class B, to grab some information from the database.

However, when the B_runtime() actually calls upon the database I get the error Cannot access protected property A::$db.

What I don’t understand is that even though I have two __construct‘s in both classes the PDO statement is being very persistent on using the database connection from class A.

I am sure this has something to do with the fact that I am running the B_runtime() from within class A because this doesn’t happen if I call it from outside of class A.

I know that I can simply change the protected $db; in class A to a public variable, however, I am really curious as to how I can fix this.

ob_start();
include('/config.php');
ob_end_clean();

$A = new A($db);
$B = new B($db);

echo $A->A_runtime();

class A{
    protected $db;
    public function __construct($db){
       $this->db = $db;
    }
    public function A_runtime(){
        return B::B_runtime();      
    }
}

class B{
    protected $db;
    public function __construct($db){
       $this->db = $db;
    }
    public function B_runtime(){
        $preparedStatement = $this->db->prepare('SELECT * FROM z_mod_html WHERE ModuleLink = :moduleid LIMIT 1');
        $preparedStatement->execute(array(':moduleid' => '1'));
        $rows = $preparedStatement->fetchAll();
        return $rows[0]['HTML'];
    }
}

Sorry for the long amount of code – if anyone has any ideas or suggestions it would be greatly appreciated. Thanks.

Answer 1

You could pass the instance of B to the method. This way you also define the dependancy of your method on class B.

$A = new A($db);
$B = new B($db);

echo $A->A_runtime($B);

class A{
    //...
    public function A_runtime($instance){
        return $instance -> B_runtime();      
    }
}

You can even use type hinting in PHP 5 to signal that you are expecting an instance of class B there:

    public function A_runtime(B $instance){