PHP Multiple Classes Extending One

Question

I have 4 classes: Main SQL Template Member . I would like SQL Template and Member to extend Main class. But also, at the same time, I would like to be able to not call all the classes neither require them all at the same time.

So, in my index.phpfile I would call Main and Template.
In my register.php page I would call Main,Template,SQL and Member.
In my submit.php page, I would call Main,SQL and Member.

I have the classes like this:

------ Main Class ------

<?php

public $db;

class Main {

    public function __construct(){
    }
    public function One(){
        // here I would call Two, Three, and Four if available
    }
}

------ SQL Class ------

<?php
class SQL extends Main {
    public function __construct(){
        parent::__construct();
        $this->db = new mysqli(....);
    }
    public function Two(){
        $this->db->query(.....);
        // Fetch query code
        echo $result;
    }
}

------ Template Class ------

<?php
class SQL extends Main {
    public function __construct(){
        parent::__construct();
        $this->db = new mysqli(....);
    }
    public function Three(){
        $this->db->query(.....);
        // Fetch query code
        echo $result;
    }
}

The Member Class would be identical to the other ones and have the function four..

So, this is how I'm doing it, but I'm not able to call functions from the child classes, only from the main.

Can you please tell me a better way of doing this? Thank you in advance.

read php.net/manual/en/language.oop5.autoload.php

Iłya Bursov
– Iłya Bursov

2013-10-15 21:59:46 +00:00
Commented Oct 15, 2013 at 21:59 — Iłya Bursov
– Iłya Bursov, Commented Oct 15, 2013 at 21:59

Fleshgrinder · Accepted Answer · 2013-10-15 22:08:06Z

3

If you really need the methods two, three and four in your Main class without implementing them you'd have to make it abstract and force the childs to implement all of them (this is absolutely acceptable and a good way of doing things like this).

<?php

abstract class Main {

  function fn1() {
    $this->fn2();
    $this->fn3();
  }

  abstract function fn2();

  abstract function fn3();

}

class Child extends Main {

  function fn2() {
    return "foo";
  }

  function fn3() {
    return "bar";
  }

}

?>

Another alternative is to check if the methods exist (not good / hack / see comment below).

<?php

class Main {

  function fn1() {
    if (method_exists($this, "fn2")) {
      $this->fn2();
    }
    if (method_exists($this, "fn3")) {
      $this->fn3();
    }
  }

  function fnDontRepeatYourself() {
    foreach (range(2,3) as $fn) {
      if (method_exists($this, $fn)) {
        $this->{$fn}();
      }
    }
  }

}

?>

The problem with the second approach is that the childs don't actually know that they have to implement the methods, that's problematic.

The inheritance should go from general to specific and you should not echo anything in your classes, rather return. There is a lot of things I could tell you now about what to do and what not, but I think it would be best for your to learn more about object oriented theory first before continuing. :)

answered Oct 15, 2013 at 22:08

Fleshgrinder

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6 Comments

user2271353 Over a year ago

So, I should have the needed-in-all classes functions in the Main one, and the other ones in the other classes, right? - I don't actually echo, I return it, and only echo one time in the final PHP file. I just did that in the example. Thank you for your help

Fleshgrinder Over a year ago

I extended my answer to include an example child class. That's good, always try to program without side effects (e.g. echo, head()) in your classes. That you need some kind of entry point where you echo your output is of course totally okay and necessary. I hope my example is from help to you, otherwise keep asking. ;)

user2271353 Over a year ago

I am having problems declaring the classes abstract. Are you able to add me on Skype and try to see the problem by TeamViewer? If so, my skype is xG.WilliamSantos

Fleshgrinder Over a year ago

Just make sure that the class is abstract <?php abstract class Name {} ?> and the methods you don't want to implement abstract function name(); that's all you have to do. Please read the manual to fully understand it, I think you have the time to do so and you will better understand everything for yourself afterwards: php.net/manual/en/language.oop5.abstract.php

user2271353 Over a year ago

It just says "Fatal error: Cannot instantiate abstract class Main". I will read the documentation, thank you.

|

phil-lavin · Accepted Answer · 2013-10-15 22:00:50Z

1

Implement Two(), Three() and Four() on your Main class. They don't necessarily have to do anything. You can then call them from within Main - they will do what is implemented in the overridden functions on the class you're calling One() on.

answered Oct 15, 2013 at 22:00

phil-lavin

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4 Comments

user2271353 Over a year ago

Can you please specify how to implement them (whith an example)? - I'm new with classes.

phil-lavin Over a year ago

In your Main class, define methods named Two, Three and Four with no implementation. E.g. public function MethodName() {}

user2271353 Over a year ago

Alright, but then I will need to call them from the class where they are overrided, right? I would like them to be called when I call the function One from the Main class.

phil-lavin Over a year ago

In your One function call the functions. E.g. $this->Two(); $this->Three(); $this->Four();

Sven · Accepted Answer · 2013-10-15 23:08:45Z

1

Don't let these classes inherit the main class. SQL, Template and Member don't have very much in common. Because of that they should not extend a common class Main, they should be on their own. The common master class would make things more complicated later on.

There is the situation that more than one class needs database access. This is when composition comes into play. The Member class should be able to read and write to the database - you should create a SQL object and pass it into the Member object. The same applies to the Template class, if the templates are also stored in the database.

My problem here is: I cannot go into the whole thing of good object oriented programming, as this would fill books, and won't be a good fit for the question-and-answer format here on Stackoverflow. So I can only suggest that you should read more stuff on the topic and avoid the God object pattern.

answered Oct 15, 2013 at 23:08

Sven

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2 Comments

user2271353 Over a year ago

Thank you for your answer. How do I "create a SQL object and pass it into the Member object"?

Sven Over a year ago

$sql = new SQL; $member = new Member($sql); - the sql object will be stored internally and can then be used by any method of Member that needs a database.

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