黑豹 ch4 ddd pattern practice (2)
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This document discusses layered architecture and repositories in domain-driven design. It covers topics like separating domain models from data models using repositories, implementing repositories to provide a collection-like interface for accessing domain objects, and differences between repositories and data access objects. The key points are that repositories mediate between the domain and data layers, encapsulate data access, and make the domain model independent of data access technologies and schemas.
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黑豹 ch4 ddd pattern practice (2)
- 1. Layered Architecture & Repository You get what you want, You use what you need
- 2. Overview Layered Architecture Repository origin DDD Repository How to implement a Repository Persistence Detail
- 3. Layered Architecture How to tackle the complexity of chagnes
- 4. View: what you want to present to your client Controller: accept requests from views and delegate to model Model: data-related logic and persistence issues MVC architecture View Controller Model
- 5. Where should we put the business logic? Controller? An ad-hoc services? Model? We need to consider the persistence first before we want to change business rules What if we have more use cases than simple CRUD? MVC architecture - When business get complex View Controller Model Primary key? Foreign key? Normalized? Change ORM Framework? Save unnecessary data Complex relationship?
- 6. Separation of concern, one focuses on business changes, one focuses on Domain model: Rich-domain Model with business logic, consists of data and behavior Data Model: Simple Object - like a data structure Separate Domain Model and Data Model View Controller Domain Model Data Model Mapper Business Logic Data + Behavior Persistence Logic Data Only
- 7. Pop quiz: Domain model or data model?
- 8. More refined layers UI Application/Controllers Domain Model Persistence Mapper Business Logic Data + Behavior Persistence Logic Data Only User Interface: Views rendered in a browser, CLI Presentation: Views, input controller Application: application controllers, application services, use cases, event listeners Domain model: Entities, Value Objects, Aggregates, domain services, domain events, POJO Persistence: Query objects, ORM, DAO Presentation
- 9. Keep your domain as pure as possible UI Application/Controllers Domain Model Persistence Mapper Presentation Interface Interface
- 10. Domain Model Application/Controllers Design Layers outside in UI Persistence Mapper Keep technical/implementation detail outside and depend inward to the business logic Presentation Interface Interface
- 11. Tell me the common part
- 12. Code Sample API Application Service Domain Model Repository Interface
- 13. Code Sample API Application Service Domain Model Repository Interface Repository Impl
- 14. Code Sample API Application Service Domain Model Repository Interface Repository Impl
- 15. Origin of Repository Where does it come from and what’s the difference between it and DAO
- 16. Debut: PoEAA by Martin Fowler Definition from Martin Fowler, PoEAA: Mediates between the domain and data mapping layers using a collection-like interface for accessing domain objects. 解決問題：將 Domain model 與 Technical persistence framework 分開，讓你 的 Domain model 可以在演變時，不被底層的技術細節影響。
- 18. When we should use repository Do we need Domain models? Object with complicated behaviors and network We don’t want persistence issues affect our business You got lots of domain object types to deal with You got lots of queries want to be encapsulated Clients need never think in SQL and can write code purely in terms of objects. Multiple data sources Change DB or version up We can leverage in-memory strategy to make tests faster
- 19. Repository give you domain models Domain Model Data Model Repository 1 2 3
- 20. Repository should be easy to use
- 21. Repository should be unaware of tech detail (different strategies) RDB Strategy InMemory Strategy
- 22. DDD Repository More restriction and design decision
- 23. Have you ever struggled? When you finish your use cases happily, but… How to read them from Database? How many data should we write into database? The data read from database it more than we need, which causes distraction in use cases How to deal with the complex network of objects
- 24. Difference Between Repository and DAO Pattern Car DAO Wheel DAO Engine DAO Seat DAO Car Repository
- 25. Difference: From What You View Car DAO Wheel DAO Engine DAO Seat DAO Car Repository engine = EngineDAO.findByCarId(id); wheels = WheelDAO.findByCarId(id); engine.activate(); wheels.roate(); car = CarRepository.get(id); car.run Customized for biz CRUD-Based
- 26. But They can Cooperate Together Car DAO Wheel DAO Engine DAO Seat DAO Car Repository
- 27. To Get a Fully-functional Car (ie. Domain Model)!!! Car DAO Wheel DAO Engine DAO Seat DAO Car Repository
- 28. ORM helps a lot Car DAO Wheel DAO Engine DAO Seat DAO Car Repository ORM/ Frame work Save() FindById()
- 29. DDD Repository Use Aggregate Roots to organize your domain models DDD Repository exists for aggregates, and treat aggregate as a unit of CRUD Read Create/Update
- 30. DDD Repository - Other Usage Get Count Generate Entity ID Collection Summaries (e.g. count on specific types of customers)
- 31. How to Design your Repository? First, target an aggregate Second, think from the use cases’ point of view Third, only exposes (public) methods you need
- 32. How to implement a Repository Step by step with coding
- 33. Key ideas A repository should be bonded to an aggregate The domain layer should be unaware of the technical details When you want to change the data source, it should be done with no sweat
- 34. Simple Repository domain/model/ICustomerRepository infrastructure/persistence/CustomerRepository
- 35. Simple Repository domain/model/ICustomerRepository infrastructure/persistence/CustomerRepository
- 36. How to reuse the code in infrastructure?
- 40. Persistence Detail Most challenging part…
- 41. How to persist an aggregate? ORM RDBMS NoSQL Raw SQL How to persistence a value object
- 42. References PoEAA by Martin Fowler https://martinfowler.com/eaaCatalog/dataMapper.html https://martinfowler.com/eaaCatalog/repository.html https://martinfowler.com/eaaCatalog/domainModel.html Pictures from https://www.pexels.com https://www.wiley.com/en-us/ Patterns%2C+Principles%2C+and+Practices+of+Domain+Driven+Design-p-9781118714706 ch25