Passing Objects into PHP constructor error

Question

Is it possible to pass an object into the constructor of a PHP class, and set that object as a global variable that can be used by the rest of the functions in the class?

For example:

class test {

   function __construct($arg1, $arg2, $arg3) {
      global $DB, $ode, $sel;

      $DB = arg1;
      $ode = arg2;
      $sel = $arg3;
   }

   function query(){
      $DB->query(...);
   }

}

When I try to do this, I get a "Call to a member function on a non-object" error. Is there anyway to do this? Otherwise, I have to pass the objects into each individual function directly.

Thanks!

Answer 1

You probably want to assign them to values on $this.

In your constructor, you'd do:

$this->DB = $arg1;

Then in your query function:

$this->DB->query(...);

This should similarly be done with the other arguments to your constructor.

$this in an instance context is how you reference the current instance. There's also keywords parent:: and self:: to access members of the superclass and static members of the class, respectively.

Answer 2

As a side-note...
Even thought this isn't required, it is generally considered best to declare member variables inside the class. It gives you better control over them:

<?php
class test {
    // Declaring the variables.
    // (Or "members", as they are known in OOP terms)
    private $DB;
    protected $ode;
    public $sel;

    function __construct($arg1, $arg2, $arg3) {
      $this->DB = arg1;
      $this->ode = arg2;
      $this->sel = $arg3;
    }

    function query(){
      $this->DB->query(...);
    }
}
?>

See PHP: Visibility for details on the difference between private, protected and public.

Answer 3

you can do it pretty easily by storing the argument as a property of the object:

function __construct($arg1, $arg2, $arg3) {
   $this->db = arg1;
}

function f()
{
  $this->db->query(...);
}

Answer 4

let's say you have a db object

$db = new db();

and another object:

$object = new object($db);

class object{

    //passing $db to constructor
    function object($db){

       //assign it to $this
       $this-db = $db;

    }

     //using it later
    function somefunction(){

        $sql = "SELECT * FROM table";

        $this->db->query($sql);

    }

}