OOP in Rails applications

Talk held on March 7, 2012, at Krakow Ruby User Group. It presents some of the OOP concepts introduced in the book 'Objects on Rails' by Avdi Grimm.

Transcript

1. OOP in Rails applications
2. MARIUSZ ŁUSIAK CTO at Applicake twitter.com/mariuszlusiak github.com/mariuszlusiak
3. Plan of action Intro Exhibits Passing methods around ActiveRecord as implementation detail Extracting a role from a model
4. Why care about OOP?
5. Ability to change
6. Don’t confine yourself
8. Exhibits
9. 1 <!-- app/views/blog/_entry.html.erb --> 2 <% if entry.image_url.present? %> 3 <%= render "/posts/picture_body", post: entry %> 4 <% else %> 5 <%= render "/posts/text_body", post: entry %> 6 <% end %>
11. 1 <article> 2 <%= entry.render_body(self) %> 3 </article>
13. 1 # app/exhibits/picture_post_exhibit.rb 2 require 'delegate' 3 class PicturePostExhibit < Exhibit 4 def render_body(context) 5 context.render(partial: "/posts/ picture_body", locals: {post: self}) 6 end 7 end
14. 1 class PostsController < ApplicationController 2 def show 3 @post = exhibit(Post.find_by_id(params[:id]), self) 4 respond_with(@post) 5 end 6 end
15. Dude, are those not presenters?
18. Exhibit characteristic
19. Exhibit characteristic Wraps a single model instance
20. Exhibit characteristic Wraps a single model instance Is a true Decorator
21. Exhibit characteristic Wraps a single model instance Is a true Decorator Brings together a model and a context
22. Exhibit characteristic Wraps a single model instance Is a true Decorator Brings together a model and a context Encapsulates decisions about how to render an object
23. Exhibit characteristic Wraps a single model instance Is a true Decorator Brings together a model and a context Encapsulates decisions about how to render an object May modify the behaviour of an object
24. Passing methods around
25. 1 class Blog 2 attr_writer :post_source 3 4 private 5 6 def post_source 7 @post_source ||= Post.public_method(:new) 8 end 9 end
26. 1 def new_post(*args) 2 post_source.call(*args) 3 end
27. How can this be useful?
28. Makes test setup easier
29. 1 blog.post_source = ->{ new_post }
30. Injecting only the dependencies we need
31. Does everyone love it?
32. ActiveRecord as implementation detail
33. Strong coupling
34. Infinite protocols
35. 1 class Post < ActiveRecord::Base 2 include FigLeaf 3 hide ActiveRecord::Base, ancestors: true, 4 except: [Object, :init_with, :new_record?, 5 :errors, :valid?, :save] 6 hide_singletons ActiveRecord::Calculations, 7 ActiveRecord::FinderMethods, 8 ActiveRecord::Relation 9 # ...
36. Any other approaches?
37. /app/domain vs /app/models
38. DataMapper pattern
39. It’s all about removing dependencies
40. Extracting a role from a model
41. God objects
42. 1 class Post 2 include Taggable 3 include RevisionControlled 4 include Permissible 5 # etc... 6 end
43. Is there a better way?
44. 1 module TaggableRecord 2 def tags 3 _tag_list 4 end 5 6 def tags=(new_tags) 7 @_tag_list = TagList.new(new_tags) 8 end 9 10 # ... 11 end
45. 1 module TaggableRelation 2 def all_tags_alphabetical 3 all_tags.alphabetical 4 end 5 6 def all_tags 7 except(:limit).map{|e| Taggable(e).tags}.reduce(TagList.new([]), &:+) 8 end 9 10 def tagged(tag) 11 select{|e| Taggable(e).tags.include?(tag)} 12 end 13 end
46. 1 def Taggable(item) 2 case item 3 when ::Class, ::ActiveRecord::Relation 4 item.extend(::TaggableRelation) 5 else 6 item.extend(::TaggableRecord) 7 end 8 end
47. 1 <article> 2 <span class="tags"><%= Taggable(entry).tags %></span> 3 </article>
48. 1 def create 2 @post = Taggable(@blog.new_post(params[:post])) 3 if @post.publish 4 redirect_to root_path, notice: "Post added!" 5 else 6 render "new" 7 end 8 end
49. 1 class PostExhibit < Exhibit 2 # ... 3 def tags 4 exhibit(Taggable(to_model).tags) 5 end 6 # ... 7 end
50. Win!
51. Any drawbacks?
52. Complex implementation
53. 1 def tagged(tag) 2 joins("JOIN item_tags ON item_tags.item_id = #{table_name}.id AND " \ 3 "item_tags.item_type = \"#{klass.name}\""). 4 joins("JOIN tags ON item_tags.tag_id = tags.id"). 5 where("tags.name = ?", tag) 6 end
54. Is it worth it?
55. Usually yes
56. Design stamina hypothesis
58. Thank you @mariuszlusiak @applicake