Nested class in php 5 - php

Question

I want to use a class inside other class.
This is my first class:
class mydb {
public function connect($host="localhost",$user,$pass,$data,$persistency=False) {
$this->host = $host;
$this->user = $user;
$this->pass = $pass;
$this->data = $data;
$this->persistency = $persistency;
$this->link=#mysql_connect($this->host,$this->user,$this->pass)or die(mysql_error());
If(($this->link) AND ($this->data)) {
If(#mysql_select_db($this->data,$this->link) or die(mysql_error())) {
return True;
}
}
return False;
}
public function query($query="",$sup="") {
If($sup) {
$query=#mysql_query($query,$this->link)or die("<br /><br />".mysql_error()."<br /><br />");
} Else {
$query=#mysql_query($query,$this->link) or die("<br /><br />".mysql_error()."<br /><br />");
}
return($query);
}
}
This is my second class:
class articles {
function getpath($id) {
$sql=$db->query("select id,name from articles where id='$id'");
$row=mysql_fetch_array($sql);
return $row['name'];
}
}
I receive this error: ( Fatal error: Call to a member function query() )

Answer 1

You didn't create $db anywhere.

Answer 2

You need to create reference to the mydb class in the articles class. Assuming you create an instance of the mydb class and stored it in the variable $db, this is what you would do.
class articles {
public static $db = null;
...
self::$db->query(...);
}
articles::$db = $db;
The variable doesn't have to be static, it could be a regular class variable. You would then reference it like
$this->db->query(...);

Answer 3

As has been mentioned, you need an instance of the mydb class made available to articles.
Here's a simple example (an anti-pattern, perhaps):
class articles {
private $db = null; // add a class property to hold your database object
// each time we create an articles object, we'll connect to the database
public function __construct() {
$this->db = new mydb(); // add your connection params
}
public function getpath($id) {
// now we can reference the object via the class property $this->db
$sql = $this->db->query("select id,name from articles where id='$id'");
$row = mysql_fetch_array($sql);
return $row['name'];
}
// the rest of your code goes here
}
If you don't want to have to constantly create new mydb instances you can do something slightly different:
Dependency Injection
class articles {
private $db = null;
// Here we'll use an existing mydb object and pass it into our new articles
public function __construct(mydb $db) {
$this->db = $db;
}
// the rest of your code goes here
}
$db = new mydb(); // create mydb
$db->connect(); // add your params
$articles = new articles($db); // create articles using mydb from above
Singleton
class mydb {
// This is static, which is special
private static $instance = null;
public static function setInstance(mydb $db) {
self::$instance = $db;
}
public static function getInstance(mydb $db) {
return self::$instance;
}
// the rest of your code goes here
}
$db = new mydb(); // Create a mydb object
$db->connect(); // add your params
mydb::setInstance($db); // store the mydb object in the mydb class
// Later when you want to query we use the stored object:
// (and this will now work everywhere in the program--
// we don't need $db anymore)
mydb::getInstance()->query();
Analysis
Generally, you don't want to open or maintain many connections to your database. It's faster to use the same connection everywhere. Sometimes this is not appropriate, though.
The singleton is a cheap form of a Service Locator.. I.e. you create a resource (or "service") and then you have a means to locate that resource without passing a variable around with you. Singletons are a basic fix, but there are better ways to architect your applications.
You might want to read about two relevant design patterns: Service Locator and Dependency Injection. Both are described here: http://martinfowler.com/articles/injection.html