PHP Keep parent class properties when using a child class constructor - php

Question

I have a parent class Database as below
class Database{
/** #var Object Filemaker object across the application*/
protected $fm = null;
public function __construct(){
if($this->fm == null){
$this->_openConnection();
}
}
/**
* Function to open connection to FileMaker
* #return null
*/
private function _openConnection(){
$this->fm = new FileMaker();
}
}
and one of my child class is
class Login extends Database{
public function validate(){
// $this->fm is accessed here with no constructors
print_r($this->fm);
}
}
I'm creating object by,
$login = new Login();
$login->validate();
Note that in this Login class, I don't have any constructor. So at the line $login = new Login(); it is calling the Database class constructor and it calls the _openConnection(). This is fine
This is my another child class:
class PouleManipulation extends Database{
private $year;
public function __construct(){
// $this->fm is only accessed if I call parent class constructor
parent::__construct();
$year = '2015';
}
public function processQueue(){
$this->fm->perform();
}
}
and
$pm = new PouleManipulation();
$pm->processQueue();
Now, when I call the $pm = new PouleManipulation();, note that I have a constructor for this class. If I access $this->fm, then it is throwing an undefined error. I googled and found that,
Inside this class constructor I need to use parent::__construct(); to access the parent class properties. If I didn't use parent::__construct(); then the parent class object is not accessible when you are having a constructor in child class
Now, the problem is in the Database class $fm is null and it again calls the _openConnection(). I have totally 10 classes extending Database class and whichever classes having the constructor it calls the _openConnection().
I need the $this->fm to be accessed across all the child classes with calling the _openConnection() only one first time and need the $this->fm in all classes well. how do you achieve this?

Answer 1

Let's clarify a bit. The properties are set on an object level. This means that everytime you instantiate a class creating an object, this object is new and has its own properties different from the others you instantiated (they may have the same value, but they're stored in different places and they're independent).
Example:
class Database {
public $fm = "Value";
}
class Login extends Database {}
class PouleManipulation extends Database {}
$a = new Login();
$b = new PouleManipulation();
$b->fm = "New Value";
echo $a->fm; // prints "Value"
echo $b->fm; // prints "New Value"
What you're looking for is a static property, which is set at a class level. It's better if you access it through a static method. Here's a quick and dirty example, but you'd better use getters and setters.
class Database {
public static $fm = "Value";
}
class Login extends Database {}
class PouleManipulation extends Database {}
$a = new Login();
$b = new PouleManipulation();
$b::$fm = "New Value";
echo $a::$fm; // prints "New Value"
echo $b::$fm; // prints "New Value"
Edit:
I used the code you provided to explain how to achieve what you want, but I want to highlight what Ryan Vincent wrote in a comment: Login class should use (not extend) a Database class