Question

I started using PHP classes and looked into OOP.

I played around by creating a Database class that looks something like this (snippet):

class Database
{

private $link;
private $result;
private $count;

    function connect()
    {
        $this->link = mysql_connect(DB_HOST, DB_USER, DB_PW);
        $return = $this->link ? 'Connected to database.' : 'Failed to connect.';
        $this->open(); // I have another function in this class to select the db
        echo $return;
    }

    function query($query)
    {
        $this->result = mysql_query($query);

    }

    function fetch()
    {
        return mysql_fetch_assoc($this->result);

    }

    function count()
    {
        $this->count = mysql_num_rows($this->result);
        return $this->count;
    }
}

Just to test, I created another class called Guestbook that looks like this:

class Guestbook
{

    function fetch()
    {
        Database::query('SELECT * FROM guestbook LIMIT 2');
        while($row = Database::fetch()){
        $result_array[] = $row;

        return $result_array;
    }   

}

Now I tested calling the functions:

$db = new Database();
$db->connect();
$db->query('SELECT * FROM test');
while($row = $db->fetch()) {
    echo $row['id'].'<br />';
}
echo $db->count();
$db->close();

This works as expected. So I went on with the Guestbook class:

$db->connect();
$guestbook = new Guestbook();
$results = $guestbook->fetch();

foreach($results as $gb) {  
    echo $gb['id'];
}

echo $db->count(); // HERE'S MY PROBLEM !

$db->close();

Everything works as I wanted, but the second time I call $db->count() it echos the previous count and not 2 (as I set LIMIT 2 in the Guestbook fetch function).

How do I interact with these classes properly, so I can use something like $db->count() globally?

Thanks in advance for any hints or solutions!

Answer 1

It is hard to give you a definitive advice on how you could wrap your database accessor with OOP and still access the count() globally.

Clearly your code is wrong.

by using the notation

Database::query

you are referring to some kind of static methods on the Database class which does not seem to be the intent here. It looks like your code does not crash because of some backward compatibility with PHP4.

you could rewrite Guestbook along this way :

class Guestbook
{

    private $db;

    function __construct(&$db) {
        $this->db = $db;
    }

    function fetch($option)
    {
        $this->db->query('SELECT * FROM guestbook LIMIT 2');
        while($row = $this->db->fetch()){
        $result_array[] = $row;

        return $result_array;
    }   

}

and then

$db = new Database();
$db->connect();
$guestbook = new Guestbook($db);
$results = $guestbook->fetch();
echo $db->count();

This technique uses a pattern known as “Dependency Injection”