PHP5 OOP scope problem

[Pig]

I have a couple classes like look something like this:

class db
{
     public function query()
     {
          //run a query...

      $this -> inc_query_count();
 }
 public function inc_query_count()
 {
      //increment query counter variable.
 }
}
class foo
{
     public function bar()
     {
          //do a bunch of stuff

      db::query();
 }
}

When db:query() is called by foo::bar(), inc_query_count() is called as well. However, it's trying to call foo:inc_query_count(), not db::inc_query_count(). What do I need to do differently to get this to work?

TIA

[Pig]

Also, I was able to sort of fix it by doing:

db :: inc_query_count()
instead of
$this -> inc_query_count()

Should I be using db:: everytime instead? Is this a good solution?

[Installer]

Probably a better way would be to have "foo" extend "db". Then your instance of "foo" will still be the calling object for "inc_query_count()", but will find it (in "db").

[Weedpacket]

One thing you should keep in mind is the difference between static (or "class") methods and instance (or "object") methods.

Object methods (and properties) belong to each object instantiated from the class - each object has its own copy of these ($this->foo, $this->bar(), etc.).

Class methods belong to the class as a whole, and not to the objects. These are the ones you refer to as someclass::foo(). They typically make up a library of functions that create objects of that class (so-called factory methods) or act on groups of objects from that class. A Set class might have a static method "Set::union(Set $a, Set $b)" for example. This is neither a method of $a nor a method of $b, but a method of the Set class itself. Methods that do stuff to objects, rather than methds that objects do stuff with, in other words.

Having a class method call $this->something() doesn't really make a lot of sense, therefore, because the class itelf doesn't have any of those methods, only its objects do.

[Pig]

Thank you weedpacket. That makes a lot more sense now.

[Pig]

OK, I want to make sure I understand this. $this -> is for for instances of objects. :: is used when you are calling methods of the class itself. Correct?

Your methods wouldn't be part of the object (not in any circumstance I can think of off the top of my head anyway). So calling a method of an external class, or just one of it's own methods would use ::.

Properties that belong to the instance of the object, and are not part of some internal operation would use $this ->.

Does that sound right? Here's a snippet I put together based off that.

<?php
class db
{
	public function query($sql)
	{
		$result = mysql_query($sql);
		return $result;
	}
	public function fetch_row($result)
	{
		$row = mysql_fetch_row($result);
		return $row;
	}
}
class article
{
	private $title;

function __construct($id)
{
	article :: load_title($id);
}

private function load_title($id)
{
	$result = db :: query("SELECT title FROM table WHERE id = $id");
	$row = db :: fetch_row($result);
	$this -> title = $row[0];
}
public function get_title($id)
{
	return $this -> title;
}
}

$db = new db;

$a = new article(1);
echo( $a -> get_title() );

$b = new article(2);
echo($a -> get_title() );

?>