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Crafted Design - ITAKE 2014


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How can we quickly tell what an application is about? How can we quickly tell what it does? How can we distinguish business concepts from architecture clutter? How can we quickly find the code we want to change? How can we instinctively know where to add code for new features? Purely looking at unit tests is either not possible or too painful. Looking at higher-level tests can take a long time and still not give us the answers we need. For years, we have all struggled to design and structure projects that reflect the business domain.

In this talk Sandro will be sharing how he designed the last application he worked on, twisting a few concepts from Domain-Driven Design, properly applying MVC, borrowing concepts from CQRS, and structuring packages in non-conventional ways. Sandro will also be touching on SOLID principles, Agile incremental design, modularisation, and testing. By iteratively modifying the project structure to better model the application requirements, he has come up with a design style that helps developers create maintainable and domain-oriented software.

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Crafted Design - ITAKE 2014

  1. 1. Crafted Design Sandro Mancuso @sandromancuso
  2. 2.  What is this application about?  What are the main concepts?  What does this application do?  What are the main features?  Where do I need to change?  Where do I put a new feature?
  3. 3.  Looking from above, I can’t see what the application does or is about  Architectural and design concepts mixed with domain  Badly structured packages/namespaces  I don’t know where to start  Classes and methods are too low level
  4. 4. Example: Layered structure
  5. 5. Example: Layered-domain structure
  6. 6. Example: MVC structure
  7. 7. MVC & MVC Variations • MVC (Smalltalk 76/80) • MVC (general concept – 1988) • Three-Tier Architecture (Presentation, Logic, Data) • MVC (Model 1/Model 2) • Model View Adapter (MVA) • Model View Presenter (MVP) • Model View ViewModel (MVVM) • Presentation-Abstraction-Control (PAC) • ….
  8. 8. MVC used badly Anaemic Domain Fat Controllers Coupling with MVC framework
  9. 9. MVC & MVC Variations They are all right. And they are wrong. It all depends on the ‘V’iew.
  10. 10. Views impact MVC structure Depending on the view technology, Views and Controllers responsibility becomes more/less coupled or blurred.  Web applications  Single-page AJAX applications with stateless backend  Console-based applications  Desktop applications  Games  Mobile / tablets  External systems (talking via Queues / Webservices) However, the model should remain unchanged.
  11. 11. MVC – A Macro Organisational Pattern Model V C M Delivery Mechanism
  12. 12. “Model” is overloaded and confusing  Model (M in MVC)  Domain Model (DDD)  View Model  Data Model  Entities & Active Record  and other artificial definitions from MVC frameworks  Associated with the persistence mechanism?
  13. 13. M => Domain Model (DDD) Domain Model combines state and behaviour, with more focus on the latter. DDD define a few building blocks to your domain:  Entities  Value Objects  Factories  Repositories  Services  Application  Domain  Infrastructure  Aggregates
  14. 14. << Web app >> Embedded Domain Model Model V C DM Delivery Mechanism Infrastructure Infrastructure DB Queue
  15. 15. Deployable Domain Model Delivery Mechanisms << external system >> << mobile app >> DB << deployable app >> Model Infrastructure DM<<W/S>> <<W/S>>
  16. 16. Event-Driven Domain Model Delivery Mechanisms DB Queue << external app 2 >> << external app 1 >> << deployable app >> Model Infrastructure DMQueue <<event 1>> <<event 2>>
  17. 17. Domain Model building blocks & responsibilities A = Action, DS = Domain Service, S = Infra. Service, R = Repository Model A 1 R 3 DS 1 DS 3 R 1 S Infrastructure Impl DM DS 2 Impl A 2 << web app >>
  18. 18. Behaviour: Action, Domain Service or Entity? Domain Service Entity Action Defines the action our domain model will be asked to perform. Behaviour related to multiple instances of the same entity or different entities. Behaviour that doesn’t fit any specific entity. Behaviour related to the data of a single instance of an entity
  19. 19. Repositories (not DAOs) Model <<repository>> Library <<repository>> Users Infrastructure <<Mongo>> Books Domain Model <<Oracle>> Users “A Repository represents all objects of a certain type as a conceptual set. It acts like a collection, except with more elaborate querying capability.” ~ Eric Evans
  20. 20. An example would be good… Order Service Orders <<interface>> Card Processor Payment ValidatorMake Payment User Account Service Usersvalid account? Payment Gatewaypay has prime account? process card validate store order Action Domain Service Infra. Service Repository Class <<interface>> Email Sender email confirmation
  21. 21. Class responsibility C A DS R cl Input Output End of code branch Produces the output End of flow First to handle input Start of the flow Execution Flow  Closer to the input: Control flow, higher level abstraction, detailed work is delegated (e.g. ProcessTrade (A), MakePayment (A)) — More suitable for Outside-In TDD (mockist).  Closer to the output / end of branch: Specific and detailed behaviour, no delegation, lower level abstraction (e.g. Parse XML (Parser), Create User (Repository)) Domain Model entry point Domain Concept entry point
  22. 22. Domain Model collaborations guideline C1 A 1 A 2 DS 1 DS 4 DS 3 R 4 R 1 cl cl cl cl C = Controller, A = Action, DS = Domain Service, R = Repository, cl = class DS 2 X A 3 R 5XC2 Except for read model X
  23. 23. Command & Query Actions << web app >> Model R DS <<Write Model>> A Model <<Read Model>> A R DB DB Queue <<domain events>>
  24. 24. So, how does the app structure look like?
  25. 25. Web project responsibility Control flow (invoke actions) JSON / XML parsers or converters View Models, validators, etc Static files Delivery Mechanism: Defines the user journey
  26. 26. Core responsibility (simple project) Tells what the system is about Tells what the system does
  27. 27. Core responsibility (bigger project) Epic / Theme Epic / Theme Epic / Theme Related domain concepts
  28. 28. What is inside model packages? Aggregate root (entity) Repository Entity (part of Book aggregate) Domain Service Value Object (part of Book aggregate) Part of aggregate behaviour Repository Value Object (part of User aggregate) Aggregate root (entity) Domain Service
  29. 29. What is inside infrastructure? Interfaces defined by the domain. Dependency Inversion Principle (DIP) CreditCardProcessor implementations Repository implementations
  30. 30. Defining testing strategies and boundaries • Unit • Integration • Acceptance • Journey • Black box • Component • System • Functional • Alpha • Beta • Conformance • … Types of tests
  31. 31. Testing strategies: User Journey Model A 1 DM A 2 << web app >> A 1 A 2 Tests the journey a user will have to do something useful in the system Application is tested as a black box normally using a BDD framework Actions are faked. We just want to know if the application presents the user with the correct journey Designed according to User Stories and Features <<fake>> <<fake>>
  32. 32. Infrastructure Impl Testing strategies: Acceptance (Action / Behavioural) A DS 1 <<mock>> RDS 2 R Tests a behaviour (action) provided by the system Action is the entry point and all external dependencies are stubbed Domain Model Normally tested using a BDD framework
  33. 33. Testing strategies: Integration Tests the classes at the system boundaries Infrastructure Impl A DS 1 <<mock>> RDS 2 R Domain Model Normally done using an in- memory Database using a unit testing framework
  34. 34. Testing strategies: Unit (Class level) Unit test at class/method level Infrastructure Impl A DS 1 RRDS 2 Domain Model DS 1 DS 2 All collaborators are mocked / stubbed (spies)
  35. 35. Testing strategies: End-to-End Model A 1 R 3 DS 1 DS 3 R 1 S Infrastructure Impl DM DS 2 Impl A 2 << web app >> Full application deployed Uses BDD framework, accessing a testing database and fake external dependencies Very few tests at this level, just to make sure application is wired properly
  36. 36. Interaction-Driven Design – IDD (Outside-In design) C A DS R cl Input Output Execution Flow  Starting from the action, model the expected behaviour (outside-in)  Entities (data structures) will emerge in order to satisfy the behaviour  Focus is on the behaviour of the system and not on how data is stored/related Design Flow
  37. 37. Answering the two original questions  What is the application about? (main concepts)  What does the application do? (main features) Expressed by nouns Expressed by verbs (Actions)
  38. 38. Thank You @sandromancuso