Is it possible to modify methods of an object instance using reflection

What I'm trying to do is create a domain model with a Plain Old PHP Object. The I'm creating a library which will do all the infrastructure stuff. So one of my models looks like this

class Project {
  public $id;
  public $name;
  public $typeId;

  private $type;

  public function getType() {
    return $this->type;
  }

  public function setType(Type $type) {
    $this->typeId = $type->id;
    $this->type = $type;
  }
}

Now if create a new Project and call setType with a valid Type object and save the project instance using the ORM both the project and type is saved. But then I load the Project and use getType method I want the ORM to have modified this method transparently to load the object from persitence. So this method here:

public function getType() {
  return $this->type;
}

to be transparently changed into:

public function getType() {
  if (is_null($this->type) {
    $this->type = $this->adapter->findById('table', $this->typeId);
  }

  return $this->type; // or return parent::getType();
}

Outlet PHP use开发者_运维问答s eval to create a Proxy class for Project called Project_Proxy but sometimes there will be subclasses of Project so I am searching for a solution by using Reflection API if there is a way.

I have search google but haven't found anyway to change a method behaviour

Edit: or would it be a good idea to use Outlet PHP's eval method to create Proxy Classes for my models and all subclasses of them?

There is no builtin way of doing this. And although you can do that using the PECL extension called runkit, I would strongly recommend finding another solution. Changing the implementation of functions you can't know anything about is very dangerous and might lead to bugs where debugging a single such bug can take longer than writing the if (is_null(... statements for all your functions.

BTW: don't use is_null(), since you might fetch null values from the database over and over again. You should store the fetched values in a separate variable.

Looking at the reflection doc on php.net, it appears to me it is impossible to modify on the flight a method.

You should try to do it in a different way.