Salve ho una classe connessione che sto costruendo :

codice:
<?php
include '../config/config.php';
/**
* 
*/
class Connessione
{
	/**
     * @var object $db_connection The database connection
     */
    private $db_connection            = null;




    
	function __construct(){
		


		session_start();


		$this->databaseConnection();




	}


	 /**
     * Checks if database connection is opened and open it if not
     */
    private function databaseConnection()
    {
        // connection already opened
        if ($this->db_connection != null) {
            return true;
        } else {
            // create a database connection, using the constants from config/config.php
            try {
                // Generate a database connection, using the PDO connector
                // @see http://net.tutsplus.com/tutorials/php/why-you-should-be-using-phps-pdo-for-database-access/
                // Also important: We include the charset, as leaving it out seems to be a security issue:
                // @see http://wiki.hashphp.org/PDO_Tutorial_for_MySQL_Developers#Connecting_to_MySQL says:
                // "Adding the charset to the DSN is very important for security reasons,
                // most examples you'll see around leave it out. MAKE SURE TO INCLUDE THE CHARSET!"
                $this->db_connection = new PDO('mysql:host='. DB_HOST .';dbname='. DB_NAME . ';charset=utf8', DB_USER, DB_PASS);
                return true;
            // If an error is catched, database connection failed
            } catch (PDOException $e) {
                $this->errors[] = MESSAGE_DATABASE_ERROR;
                return false;
            }
        }
    }


    public function get_databaseConnection(){


    	return $this->db_connection;
    }
	
    public function eseguiqueryfetch($sql){


     	
        if($this->get_databaseConnection()){


            //Eseguo la query
            $statement = $this->get_databaseConnection()->query($sql); 
                    
            $result = $statement->fetch(PDO::FETCH_ASSOC);
            
            return $result;
        }
        else{
            echo'errore';
        }
        
     
    }




     public function contaRighe($sql){
        $connessione=$this->get_databaseConnection();
            
        //Preparo la query
        $query = $connessione->prepare($sql); 


        //eseguo la query 
        $query->execute();


        //conto le righe
        $count = $query->rowCount();


        return $count;


     }




}






?>
Richiamando in una pagina esterna il metodo eseguiqueryfetch($sql)

ho il seguente errore , premetto che la connessione è presente e che la stringa sql inserita in php admin funziona....

Quale è l'errore

Call to a member function fetch() on a non-object in /membri/my_site/classes/Connessione.php on line 65