STOP! Use case time!

A brief introduction about DCI on Ruby on Rails.

Transcript

1. STOP! Use case time! Or, a brief introduction to DCI.
2. Who am I? André Medeiros Rubyist for 7+ years @superdealloc github.com/andremedeiros quintel.com
3. What’s DCI?
4. How I develop apps •UI first approach •UI directly maps to operations within the code •MVC doesn’t always conform to this standard of development
7. DCI is great for this approach Invented by Trygve Reenskaug Comes in where MVC fails: capturing behavior Places interaction in obvious places Models represent entities, not behavior Splits what an object is from what it does
8. D is for Data What the object is Persistence Structure
9. C is for Cookie Context Class which enacts one or more use cases Instantiated by a user action Mixes in participating objects with Roles Responsible for acting out the use case
10. I is for Interaction What the system does Logic is contained in Role modules Implemented by mixing in objects with Roles in a given Context or use case
11. How it works Controller Context starts use case
12. How it works Controller Context starts use case Context Object(s) finds or creates the participating objects
13. How it works Controller Context starts use case Context Object(s) mixes in all the roles needed Role Role Role
14. How it works Controller Context starts use case Context Object(s) invokes the role methods Role Role Role
15. Code Samples
16. # app/controllers/transfers_controller.rb (before DCI) class TransfersController def create @source = Account.find(params[:source_id]) @destination = Account.find(params[:dest_id]) @source.balance -= params[:amount] @destination.balance += params[:amount] end end
17. # app/controllers/transfers_controller.rb (after DCI) class TransfersController def create @source = Account.find(params[:source_id]) @destination = Account.find(params[:dest_id]) mt = MoneyTransfer.new(@source, @destination) mt.execute(params[:amount]) end end
18. # app/contexts/money_transfer.rb class MoneyTransfer def initialize(source, destination) @source = source @destination = destination assign_transferrer(@source) end def execute(amount) @source.transfer_to(@destination, amount) end private def assign_transferrer(account) account.extend(Transferrer) end module Transferrer def transfer_to(destination, amount) self.balance -= amount destination.balance += amount end end end
19. And what about tests? You do write tests, right? RIGHT?!
20. # spec/controllers/transfers_controller_spec.rb (before) describe TransfersController do describe 'POST create' do before(:each) do @s = FactoryGirl.create :account, balance: 500 @d = FactoryGirl.create :account, balance: 1000 end it 'should transfer money between accounts' do post :create, format: :json, source: @s.id, destination: @d.id, amount: 500 # Yikes :-( [ @s, @d ].map(&:reload) expect(response.status).to eq(201) expect(@s.balance).to eq(0) expect(@d.balance).to eq(1500) end end end
21. # spec/contexts/money_transfer_spec.rb (after DCI) describe MoneyTransfer do ! before(:each) do ! ! @source = OpenStruct.new(balance: 500) ! ! @destination = OpenStruct.new(balance: 1000) ! end ! ! it 'should move money between accounts' do ! ! MoneyTransfer.new(@source,@destination).execute(500) ! ! ! ! expect(@source.balance).to eq(0) ! ! expect(@destination.balance).to eq(1500) ! end end
22. Advantages Keeps the model slim (fat != obese) Business logic is easy to find and track down Facilitates reusability Highly testable
23. FUD Object#extend kills kittens
24. FUD Concerns do the exact same thing It’s not real OO Makes you write more code
25. Questions?