Can PDO connections be maintained between classes?

Question

I'm attempting to make a simple query library and I'm using PDO for database access.

Let's say I have the following two classes:

class FirstClass {
    var $dbh;

    function __construct($host,$dbname,$user,$pw) {
        $this->dbh = new PDO ("mysql:host=$host;dbname=$dbname",$user,$pw);
    }

    function use_second($foo) {
        return new SecondClass ($foo,$this->dbh);
    }
}

class SecondClass {
    function __construct($foo, $dbh) {
        $sth = $dbh->prepare('SELECT * FROM atable WHERE bar = :foo');
        $sth = $sth->execute(array('foo'=>$foo));
        // do something with the query
    }
}

Is this the correct way to use the same PDO connection between classes? - Because I seem to be having some issues with this, for example, if I var_dump my connection from the second class, I get:

object(PDO)#2 (0) { }

Surely that isn't right?

Also if I run a select query, and then dump the $sth variable, I just get:

bool(true)

Is this because I am handling the connection incorrectly? - If so how can I properly use the same connection between classes?

Answer 1

This happens, because you overwrite $sth, which was your statement, but now is a boolean:

class SecondClass {
    function __construct($foo, $dbh) {
        // returns PDOStatement:
        $sth = $dbh->prepare('SELECT * FROM atable WHERE bar = :foo');
        // returns boolean:
        $sth = $sth->execute(array('foo'=>$foo));
        // do something with the query
    }
}

To correct it, just do not overwrite $sth, so you are able to fetch results from it:

class SecondClass {
    function __construct($foo, $dbh) {
        // returns PDOStatement:
        $sth = $dbh->prepare('SELECT * FROM atable WHERE bar = :foo');
        // returns boolean:
        $success = $sth->execute(array('foo'=>$foo));
        // do something with the query
        if ($success) {
            // do something with $sth->fetchAll() or $sth->fetch(), or anything
            $all_the_results = $sth->fetchAll();
        };
    }
}