Question

Is it possible to keep all my database related configuration (hostnames, usernames, passwords, and databases) as well as the function to connect to and select the correct database in a separate class?

I tried something like this:

class Database
{
    var $config = array(
        'username' => 'someuser',
        'password' => 'somepassword',
        'hostname' => 'some_remote_host',
        'database' => 'a_database'
    );
    function __construct() {
        $this->connect();
    }
    function connect() {
        $db = $this->config;
        $conn = mysql_connect($db['hostname'], $db['username'], $db['password']);
        if(!$conn) {
            die("Cannot connect to database server"); 
        }
        if(!mysql_select_db($db['database'])) {
            die("Cannot select database");
        }
    }
}

And then in another class I would use in the classes __construct function:

require_once('database.php');
var $db_conn = new Database();

But this doesnt save the connection, it ends up defaulting to the servers local db connection. Or do I have to do the database commands everytime before I execute some database commands?

Answer 1

I modified your class to work as you seem to be expecting it to:

<?php
class Database
{
    var $conn = null;
    var $config = array(
        'username' => 'someuser',
        'password' => 'somepassword',
        'hostname' => 'some_remote_host',
        'database' => 'a_database'
    );

    function __construct() {
        $this->connect();
    }

    function connect() {
        if (is_null($this->conn)) {
            $db = $this->config;
            $this->conn = mysql_connect($db['hostname'], $db['username'], $db['password']);
            if(!$this->conn) {
                die("Cannot connect to database server"); 
            }
            if(!mysql_select_db($db['database'])) {
                die("Cannot select database");
            }
        }
        return $this->conn;
    }
}

Usage:

$db = new Database();
$conn = $db->connect();

Note that you can call connect() as many times as you like and it will use the current connection, or create one if it doesn’t exist. This is a good thing.

Also, note that each time you instantiate a Database object (using new) you will be creating a new connection to the database. I suggest you look into implementing your Database class as a Singleton or storing it in a Registry for global access.

You can also do it the dirty way and shove it in $GLOBALS.

Edit

I took the liberty of modifying your class to implement the Singleton pattern, and follow the PHP5 OOP conventions.

<?php
class Database
{
    protected static $_instance = null;

    protected $_conn = null;

    protected $_config = array(
        'username' => 'someuser',
        'password' => 'somepassword',
        'hostname' => 'some_remote_host',
        'database' => 'a_database'
    );

    protected function __construct() {
    }

    public static function getInstance()
    {
        if (null === self::$_instance) {
            self::$_instance = new self();
        }
        return self::$_instance;
    }

    public function getConnection() {
        if (is_null($this->_conn)) {
            $db = $this->_config;
            $this->_conn = mysql_connect($db['hostname'], $db['username'], $db['password']);
            if(!$this->_conn) {
                die("Cannot connect to database server"); 
            }
            if(!mysql_select_db($db['database'])) {
                die("Cannot select database");
            }
        }
        return $this->_conn;
    }

    public function query($query) {
        $conn = $this->getConnection();
        return mysql_query($query, $conn);
    }
}

Usage:

$res = Database::getInstance()->query("SELECT * FROM foo;");

or

$db = Database::getInstance();
$db->query("UPDATE foo");
$db->query("DELETE FROM foo");