class within another class - php

Question

I am new to PHP OOP and would like to try to nest several classes within another class, to latter call them like so:
$sql = new SQL();
$sql->Head()->Description($_SESSION['page']);
//OR
$sql->Head()->Keywords($_SESSION['page'])
//OR
$sql->Body()->Clients($_SESSION['client'])
//ETC
$query = $sql->Run(); // equivalent to mysql_query("...");
As you can guess, I run into some problems and ended with this poor code:
<?php
require( $_SERVER['DOCUMENT_ROOT'] . '/#some_db_directory/database.php');
//This file contains $db['host'], $db['user'], etc...
class SQL {
public $sql;
public function __construct() {
global $db;
}
public class Head() {
public function Description($page) {
return "SELECT * FROM `$db['database']`.`desciption` WHERE `page` = '$page'";
}
public function Keywords($page) {
return "SELECT * FROM `$db['database']`.`keywords` WHERE `page` = '$page'";
}
}
}
$sql = new SQL();
echo $sql->Head()->Description('home'); //For testing
Is it possible to nest classes in PHP?
If so, how is it done?

Answer 1

What you are trying to do is called Encapsulation. Try google search on PHP encapsulation to learn more.
Here is a code example from http://www.weberdev.com/get_example.php3?ExampleID=4060,
<?php
class App {
private static $_user;
public function User( ) {
if( $this->_user == null ) {
$this->_user = new User();
}
return $this->_user;
}
}
class User {
private $_name;
public function __construct() {
$this->_name = "Joseph Crawford Jr.";
}
public function GetName() {
return $this->_name;
}
}
$app = new App();
echo $app->User()->GetName();
?>

Answer 2

I'm assuming that database.php is a database class. In that case you could do something like this.
head.php
Class Head{
private $_db;
private $_dbName;
public function __construct($db, $dbName){
$this->_db = $db;
$this->_dbName = $dbName;
}
public function Description($page) {
$results = $this->_db->query("SELECT `text` FROM `$this->_dbName`.`description` WHERE `page` = '$page'");
return '<meta name="description" content="' . $results['text'] . '">';
}
public function Keywords($page) {
$results = $this->_db->query("SELECT * FROM `$this->_dbName`.`keywords` WHERE `page` = '$page'");
$keywords = array();
foreach($results as $result){
array_push($keywords, $result['word']);
}
return '<meta name="keywords" content="' . implode(',', $keywords) . '">';
}
}
sql.php
require( $_SERVER['DOCUMENT_ROOT'] . '/#some_db_directory/database.php');
// Require head class file
require( $_SERVER['DOCUMENT_ROOT'] . '/#some_db_directory/head.php');
Class SQL{
public $Head;
public function __construct($dbName){
global $db;
$this->Head = new Head($db, $dbName);
}
}
You would then pass the name of the database into the SQL class (which propogates through to the Head class).
// Require the sql class file
require( $_SERVER['DOCUMENT_ROOT'] . '/#some_db_directory/sql.php');
$sql = new SQL('mydatabase');
echo $sql->Head->Description('home');
Again note that your database class might not return results the way I'm using them here. You will have to modify this to work with your particular database class.

Answer 3

Try it like this
<?php
require( $_SERVER['DOCUMENT_ROOT'] . '/#some_db_directory/database.php');
//This file contains $db['host'], $db['user'], etc...
class SQL {
public $sql;
private $_head;
public function __construct() {
global $db;
$_head = new HeadClass();
}
public function Head() {
return $this->_head;
}
}
class HeadClass { // Class cannot have a public access modifier
public function Description($page) {
return "SELECT * FROM `" . $db['database'] . "`.`desciption` WHERE page = $page";
}
public function Keywords($page) {
return "SELECT * FROM `" . $db['database'] . "`.`keywords` WHERE page = $page";
}
}
$sql = new SQL();
echo $sql->Head()->Description('home.html');
?>
I am moving the class declaration outside the class and creating an instance of the class with in SQL. This is then made available via the Head() function.
Note: For body you will need to create a separate class and use a reference in the SQL class to it like I have done for head.