Introduction to Decorator and Presenter Design Pattern in Rails

1. Presenter & Decorator
In Rails

2. Decorator

3. What is Decorator in Rails?

4. A decorator is a design pattern. Its intent, as
described in Design Patterns by the Gang of Four
is:
> Attach additional responsibilities to an object
dynamically. Decorators provide a flexible
alternative to subclassing for extending
functionality.

5. Why do we use Decorator?

6. ● Refactoring for SRP (Single Responsibility
Principle)
● Extend behaviors of an object

7. Try out #1
● I have a coffee class which has #cost method.
Class Coffee
def cost
2
end
end
coffee = Coffee.new()
coffee.cost
#=> 2
● What if I want to add sugar or milk? Assume sugar
price is 0.2 and Milk is 0.4

8. How to implement Decorator?

9. There is a great post by Dan Croak on how to
implement Decorator in rails.
http://robots.thoughtbot.com/post/14825364877/e
valuating-alternative-decorator-implementations-in

10. When to use Decorator?

11. ● When an object knows too much.
● When a group of methods describe a possible
meaning of behavior
● When want to extend behavior of an object
● When fully understand Decorator

12. Presenter

13. What is Presenter in Rails?

14. ● A form of Decorator
● A bridge between the model and view in
presentation logic

15. Why do we use Presenter?

16. ● To cleanup views by moving aways all the logic
● To keep all presentation logic in one place

17. How to implement Presenter?

18. There is a great post by Harold Giménez on how
to implement Presenter in rails.
http://robots.thoughtbot.com/post/13641910701/ti
dy-views-and-beyond-with-decorators

19. Don't confuse with helper with
Presenter

20. ● Simple logic goes to helper
● Logic that don't relate to object, goes to helper
● Logic relate to object, goes to Presenter
● Too complex logic can also go to Presenter

21. Q & A

22. Thanks You