DCI - The End User Architecture

Mike Pack

@zombidev

Overview

• - Current state of Rails practices
• - Fat controllers
• - Data, Context and Interaction (DCI) foundation
• - DCI example
• - Conclusion

Monolithic Rails Model

• - <code>
• - "Fat models, skinny controllers"
• - Rails models are obese!
• - Monolithic and difficult to maintain
• - Persistence intermixed with domain logic

Monolithic Rails Model

Skinny Controllers

• - But why? Large controllers are:
• - Unmaintainable
• - Not modular

Overview

• - Current state of Rails practices
• - Fat controllers
• - Data, Context and Interaction (DCI) foundation
• - DCI example
• - Conclusion

Fat Controllers

Decoupling Fat Controllers

Overview

• - Current state of Rails practices
• - Fat controllers
• - Data, Context and Interaction (DCI) foundation
• - DCI example
• - Conclusion

Data, Context and Interaction

DCI - Motivation/Foundation

• - Build on principles of Lean and Agile
• - Represent the "end user's mental model" in code
• - Work from the outside-in, akin to BDD
• - Decouple persistence ("what the system is") and function ("what the system does")

• "what the system is" changes infrequently
  
• "what the system does" changes often
  

DCI - Overview

Overview

• - Current state of Rails practices
• - Fat controllers
• - Data, Context and Interaction (DCI) foundation
• - DCI example
• - Conclusion

User Stories

• - represent the end user's goal
• - fit directly into Agile
• - give us a starting point for development
• - expose what the system is ("publisher" and "blog post")
• - expose what the system does ("publish a blog post")

Data, Context and Interaction

Interaction = Roles

Data, Context and Interaction

Interaction = Roles

"What the system does"

          module Publisher
            def publish(post)
              post.publish
            end
          end
        

• - contain the "actions" performed by actors
• - define what the system does

Data, Context and Interaction

Connects data objects with roles

Data, Context and Interaction

Connects data objects with roles

          class UserPublishesPostContext
            def initialize(user, post)
              @publisher, @post = user, post
              @publisher.extend Publisher            # extend instance!
            end
            def call
              @publisher.publish(@post)
            end
          end

          # Within the controller...
          @user = current_user
          @post = Post.find(params[:id])
          UserPublishesPostContext.new(@user, @post).call
        

Data, Context and Interaction

Connects data objects with roles

• - be invoked from within the controller
• - extend data with roles: @publisher.extend Publisher
• - call the necessary action: @publisher.publish(@post)

Data, Context and Interaction

Data = Rails Models

Data, Context and Interaction

Data = Rails Model

"What the system is."

          class Post < ActiveRecord::Base
            validates :title, :presence => true
            
            def publish
              update_attribute(:published_at, Time.zone.now)
            end
          end
        

• - be extremely dumb and logicless
• - expose getters and setters
• - know nothing about how it's used

Overview

• - Current state of Rails practices
• - Fat controllers
• - Data, Context and Interaction (DCI) foundation
• - DCI example
• - Conclusion

What the system is
vs
What the system does

DCI Will Help You...

• - Decouple domain logic from persistence
• - Improve testability
• - Create readable code (file names and file structure)
• - Allow for change as the application grows
• - Represent the end user mental model in code

This is an intro...there's more...

Let's talk about it.

Thanks

@zombidev