Data Context Interaction - What is it good for?
2 likes3,020 views
DCI is an architectural pattern that aims to cleanly separate code for system behavior from code representing the domain model. It focuses on modeling interactions rather than classes. In DCI: - Data represents the domain model and is stable over time. - Context enacts a specific use case by mixing roles into participating objects. - Interaction defines methods that carry out the use case by being mixed into role modules. - A controller starts a use case by instantiating a context, which finds objects and mixes in roles to execute the interaction methods. DCI aims to give interactions first-class status in the code and provide an object-oriented view of use cases that is closer to how people think about
Data Context Interaction - What is it good for?
- 1. Data Context Interaction What is it good for? Markus Nordin @mnordin
- 2. Disclaimer I will for the next 30 minutes talk smack about MVC But i secretly <3 MVC
- 3. History of DCI Trygve Reenskaugs ideas about role based modeling in early 2000 (same guy who invented MVC in the late seventies) Working design model in 2006 Working prototype in mid 2008 Complement to MVC
- 4. Why DCI? MVC fails to capture behaviour There's no apparent place to put interactions (exception: simple actions that involves a single object) Model should represent things Things should be stable Natural difference between what an object is and what it does. Why not in the code?
- 5. Goals with DCI Giving system behaviour first class status Cleanly separate code for rapidly changing behavior from code for slowly changing domain knowledge Object style of thinking that is close to peoples mental models rather than class style
- 6. Data What the system is Closely corresponds to the Model Reflects the domain structure rather than behaviour
- 7. Context Context is a class (instance) which enacts one (or more) use cases Instantiated by a user (controller) action Mixes in participating objects with Roles The context is responsible for acting out the use case
- 8. Interaction What the system does Methods in role modules Implemented by mixing in objects with Roles in a given Context or use case
- 9. Executing DCI Controller action starts a use case by instansiating a context class The context finds (or creates) the objects that are participating in the use case The context mixes in all the roles needed into the objects The context invokes the role methods on the objects and starts the use case enactment
- 10. Money transfer example Bank - send money to another account SendMoneyContext account account SourceAccount DestinationAccount send(amount) verify(amount) deposit(amount)
- 11. My implementation Training app Attend a training event UserAttendsEventContext user event AttendingRole PublicEventRole attends(event) attend_on_google(user)
- 12. What is it good for? Kind of awkward to deal with context instances - bad implementation? Class methods belonging to roles or object? Simple console usage must also follow the context Easy to find specific methods (if used consistently) Fat models go on crash diet! Easy to maintain Easy to follow an entire use case
- 13. Questions? Do we need DCI?