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Crafted Design - GeeCON 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 product requirements, he has come up with a design style that helps developers create maintainable and domain-oriented software.

Published in: Software, Technology, Education
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Crafted Design - GeeCON 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 What does this application do? What is it about?
  5. 5. Example: Layered-domain structure Books and Users. Cool, but what does this application do?
  6. 6. Example: MVC structure Awesome. It’s a web application. So?
  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 wrong. But they are also right. 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 – Responsibilities UC = Use Case, DS = Domain Service, S = Infra. Service, R = Repository Model UC 1 R 3 DS 1 DS 3 R 1 S Infrastructure Impl DM DS 2 Impl UC 2 << web app >>
  18. 18. 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
  19. 19. Command & Query Use Cases << web app >> Model R DS <<Write Model>> UC Model <<Read Model>> UC DB DB Queue <<domain events>>
  20. 20. So, how does the app structure look like?
  21. 21. Web project responsibility Control flow (invoke use cases) JSON / XML parsers or converters Page Objects, validators, etc Static files
  22. 22. Core responsibility (simple project) Tells what the system is about Tells what the system does
  23. 23. Core responsibility (bigger project) Epic / Theme Epic / Theme Epic / Theme Related domain concepts
  24. 24. 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
  25. 25. What is inside infrastructure? Interfaces defined by the domain. Dependency Inversion Principle (DIP) CreditCardProcessor implementations Repository implementations
  26. 26. Domain Model collaborations guideline C UC 1 UC 2 DS 1 DS 3 DS 2 R 3 R 1 cl cl cl cl C = Controller, UC = Use Case, DS = Domain Service, R = Repository, cl = class
  27. 27. Class responsibility C UC DS R cl DB 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 (UC), MakePayment (UC)) — 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
  28. 28. Defining testing strategies and boundaries • Unit • Integration • Acceptance • Journey • Black box • Component • System • Functional • Alpha • Beta • Conformance • … Types of tests
  29. 29. Testing strategies: User Journey Model UC 1 DM UC 2 << web app >> UC 1 UC 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 Use cases are facked. We just want to know if the application presents the user with the correct journey Designed according to User Stories and Features <<fake>> <<fake>>
  30. 30. Infrastructure Impl Testing strategies: Acceptance (Action / Behavioural) UC DS 1 <<mock>> RDS 2 R Tests a behaviour (action) provided by the system Use Case is the entry point and all external dependencies are stubbed Domain Model Normally tested using a BDD framework
  31. 31. Testing strategies: Integration Tests the classes at the system boundaries Infrastructure Impl UC DS 1 <<mock>> RDS 2 R Domain Model Normally done using an in- memory Database using a unit testing framework
  32. 32. Testing strategies: Unit (Class level) Unit test at class/method level Infrastructure Impl UC DS 1 RRDS 2 Domain Model DS 1 DS 2 All collaborators are mocked / stubbed (spies)
  33. 33. Testing strategies: End-to-End Model UC 1 R 3 DS 1 DS 3 R 1 S Infrastructure Impl DM DS 2 Impl UC 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
  34. 34. Outside-In vs. Classic TDD  The closer to the input a class is, the more flow control and delegation it does.  The closer to the output a class is, the more specific and less delegation it does. Using Outside-in TDD starting from Controllers and/or Use Cases. Model UC 1 R 3 DS 1 DS 3 R 1 S Infrastructure Impl DM DS 2 Impl UC 2 << web app >>
  35. 35. 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)
  36. 36. Thank You @sandromancuso