1. High-Performance Distributed Systems withCommand/Query Responsibility Segregation Jonathan Oliver Utah Code Camp 2010

2. Think Differentlier Best practices != best thinking Blind vs intentional application Question everything How much does it cost?

3. Domain Muddling and Modeling What was the original intent? Screen-based aggregate roots? Show domain state? Validation? Get/set, go!

4. Distributed Systems Architecture

5. Optimistic and Pessimistic Stalemate Collaborative users Current state? Get data Get data Stale data Update data

6. Layeringitis Why go through all the layers?

7. Tiers for Fears Why transform across the tiers? DTOs: more code, tests, maintenance, $$$ Pre-transformed?

8. CQRS: Gotta Keep ‘Em Separated SOLID, Architectural “S”

9. Query Query Quite “Contrery” Showing data Query-only storage KISS, YAGNI If it’s stale anyway List of Customers --------------------- --------------------- --------------------- (from 10 minutes ago)

10. All Your Database Are Belong To Us Screen-based views UnDRY your data—data duplication “Persistent View Model” Storage/database requirements Scaling out SELECT * FROM Carts WHERE ID = 456;

11. Queries: Summary Stale data “Persistent View Model” For queries only One table per view Updated by events Data duplication is good No table relationships No foreign keys

12. Command & Conquer Say what? What is a command? Intention revealing SaveInvoicevsPlaceOrder SaveCustomervsMakeCustomerDelinquent

13. UI Design Excel-based UIs Task-based UIs

14. This Time It’s Gonna Be Different Can we fully trust user decisions?

15. Commands and Validation Validation Is the input potentially good? Ranges, lengths, etc Fail fast Leverage persistent view model Unique emails? Decides if a command should be sent Enables high probability of success

16. Business Rules Should we do this? Based upon the current system state

17. Commands: Summary Expresses intent Reply is: “Thank you, we’ve received your input.” Asynchronous Amazon Netflix

18. Domain Models, Take 2 Commands already validated No relationships for reading Only persists what it needs Behavior: Give discounts to high-volume customers

19. The Big Picture Image courtesy Udi Dahan

20. The Big Picture: Summary Simple 2-tier queries Commands express intent Task-based UI captures intent Smaller, more focused pieces

21. Questions?