Question

I have a dilemma on how to implement states for objects.
Let’s say we have this:

class User {

     private $_active;// 1 or 0
     private $_deleted;// 1 or 0
     ...

}

These properties – as I see it – imply a state on User object.
What I would like to do is to define some events like afterActivate() or afterDelete() so I can chain my routines. I.e. after activation update some counters, after deletion also update some counters…

So I’m considering two approaches at the moment – first one is to create classes Activable and Deletable ( don’t mind the naming ) and then make User inherit those classes through a hierarchy of inheritance.

class Activable {

    protected afterActivate(){};

}

class Deletable {

    protected afterDelete(){};
}

class Activable extends Deletable {}
class User extends Activable{}

There are two problems that I see with this approach – first one is that class Activable now has implied Deletable state which is wrong and second problem is – if I have more states – 5-6 states the inheritance hierarchy may become quite complex. ( because User will extend the model class which will extend something else etc…)

The second approach is to use traits in PHP and use them to achieve this.
So I would have something like

class User{
    use Activable, Deletable; 

}

What approach would be better – maybe some 3rd approach?
Am I going in the right direction here?

Thanx.

Answer 1

Usually you would use Marker Interfaces for this sort of thing.
I suppose this is some kind of ORM we’re talking about? Than I also assume there is some kind of object handling the persistence of your entities. Let that object check that $entity instanceof Deletable and act upon that.