STOP! Use case time!
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This document provides an introduction to the Domain-Context-Interaction (DCI) software architectural pattern. It begins by introducing the presenter and their experience with Ruby. It then discusses how DCI is commonly brought up in discussions of Ruby development. The key aspects of DCI are explained - models represent entities, contexts enact use cases by mixing in roles, and roles define interactions. Code samples are shown to illustrate how DCI separates concerns compared to a more traditional MVC approach. Advantages of DCI like modularity, testability and reusability are listed. Finally, common criticisms of DCI are addressed and questions from the audience are invited.
![class TransfersController
def create
@source = Account.find(params[:source_id])
@destination = Account.find(params[:dest_id])
@source.balance -= amount
@destination.balance += amount
end
end
Wednesday, January 9, 13](https://image.slidesharecdn.com/dci-130108192830-phpapp02/85/STOP-Use-case-time-18-320.jpg)
STOP! Use case time!
- 1. STOP! Use case time! Or, a brief introduction to DCI. Wednesday, January 9, 13
- 2. Who am I? André Medeiros Rubyist for 7+ years @superdealloc github.com/andremedeiros quintel.com Wednesday, January 9, 13
- 3. You’ve probably heard of it Wednesday, January 9, 13
- 4. You’ve probably heard of it Wednesday, January 9, 13
- 5. You’ve probably heard of it Wednesday, January 9, 13
- 6. You’ve probably heard of it “DCI in Ruby is completely broken” - Tony Arcieri (@bascule) “Rails Developers Should Take DCI Seriously” - Giles Bowkett (@gilesgoatboy) Wednesday, January 9, 13
- 7. Wednesday, January 9, 13
- 8. 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 Wednesday, January 9, 13
- 9. 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 Wednesday, January 9, 13
- 10. D is for Data What the object is Persistence Structure Wednesday, January 9, 13
- 11. 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 Wednesday, January 9, 13
- 12. 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 Wednesday, January 9, 13
- 13. How it works Controller starts use case Context Wednesday, January 9, 13
- 14. How it works Controller starts use case Context finds or creates the Context participating objects Object(s) Wednesday, January 9, 13
- 15. How it works Controller starts use case Context Context Object(s) mixes in all the roles needed Role Role Role Wednesday, January 9, 13
- 16. How it works Controller starts use case Context Context Object(s) invokes the role methods Role Role Role Wednesday, January 9, 13
- 17. Code Samples Wednesday, January 9, 13
- 18. class TransfersController def create @source = Account.find(params[:source_id]) @destination = Account.find(params[:dest_id]) @source.balance -= amount @destination.balance += amount end end Wednesday, January 9, 13
- 19. 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 Wednesday, January 9, 13
- 20. Advantages Keeps the model slim (fat != obese) Business logic is easy to find and track down Facilitates reusability Highly testable Wednesday, January 9, 13
- 21. FUD Object#extend kills kittens Wednesday, January 9, 13
- 22. FUD Concerns do the exact same thing It’s not real OO Makes you write more code Wednesday, January 9, 13