should I have logic in my model class or other classes

Question

I just want to have other opinions about this one that I have been debating in my head, for example I have class user_controller, and class user

class User
   attr_accessor :name, :username   
end

class UserController
   // do something about anything about users
end

The question would be should I have logic in my User class so it would be

user = User.new
user.do_something(user1)

or it should be 

user_controller = UserController.new
user_controller.do_something(user1, user2)

I'm not sure which one is the best design, I personally quite like the first one so for example it would read like

john = User.new
john.accept_friend(jane)

instead of 
user_controller = UserController.new
user_controller.accept_friend(john, jane)

What are pros and cons of those patterns? This is not just specific to Ruby, it's because I thing ruby is easier in typing.

Edit: There is really good conversion going on, but I quite like to here more from people. Thanks everyone.

Answer 1

Yes, you should keep logic in your model! That is, if you do actual object oriented programming (and it looks like you do). To quote Wikipedia:

Object-oriented programming (OOP) is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs.

This is especially true if you're trying to do domain driven design (which your tags imply). DDD is all about expressing your domain with objects.

Martin Fowler says putting the logic outside your model is an anti-pattern.

Answer 2

Most people would say that you should not keep logic in your model-classes. Exceptions might include:

• helper functions accessing a contained Collection (addToList(Object o), getFromList(int index), etc etc)
• Standard Object and similar overrides (equals, hashCode, toString, clone, compareTo, etc)
• Data pre/post processing (like fixing strings to uppercase or stuff like that)

Since people won't expect there to be logic in model classes, you should probably avoid it too. It will confuse other developers who might have to look at and maintain your code in the future. After all, that is why there are patterns - to help other developers recognize and maintain your code.