Am I missing something about the use of PHP's PDO?

Here's a simple piece of code I'm writing:

class LessonsLearntServiceTyped
{
    private $username = "***********";
    private $password = "***********";
    private $dsn      = "mysql:dbname=lessonslearnt;host=****
******.db.******.hostedresource.com";
    private $dbh;


    public function __construct(){
        try{
            $dbh = new PDO($this->dsn, $this->username, $this->password);

        }catch(PDOException $e){
            echo "Connection failed: ".$e->getMessage();
        }
    }



     public function returnAllEntries(){
        $query = "select * from lessons_learnt order by id";

    }

}

OK. I've not had much experience with PDO before but I've seen some examples on the net and apparently you can't serialize or de-serialize a PDO object.(that's the error message I get when I try to set a PDO object to an instance variable so that I can use it later)

Well, if we can't have PDO objects as instance variables, how then will I proceed on to writing the returnAllEntries() method? Will I have 开发者_Python百科to create the PDO object again so I can use it there??(and also a new PDO object for each function I write that deals with the database)?

What am I missing here?

Thank you all in advance

EDIT

$this->dbh = new PDO($this->dsn, $this->username, $this->password); is what I wanted to do.

But when I do that I get the following error message:note this error message comes from the PHPUnit console which I'm using to tunit-test this class. In the browser it doesn't show any errors.

""You cannot serialize or unserialize PDO instances"

It looks like this is a very very weird edge case with exceptions from reading this:

http://fabien.potencier.org/article/9/php-serialization-stack-traces-and-exceptions

Try taking out the $e->getMessage() line bit in your catch statement and see if it changes anything.

I think the problem was with my instance of PHPUnit test runner.