Model Pollution

Transcript

1. Starring Directed By Special Appearance Presented by With Model Pollu)on is Bad— What Can I Do about It?
3. !
4. Hi, I’m Henning
5. !"#
8. @hschwentner So!ware != End in itself
9. @hschwentner ! ! " Software is build Tech people business people # " for for by
10. @hschwentner Programming 1. Learn about a domain 2. Build a model for it 3. Add technology to build the system: • programming language • UI • database • …
11. @hschwentner Example: A Banking Domain bank account customer teller computer transaction
12. @hschwentner Example: A Banking Domain computer Banking 3000
14. https://hschwentner.io Read on in:
15. @hschwentner Rules of thumb:
16. Objects from real world turn into objects in so!ware
18. Actions from real world turn into operations in so!ware
20. => Object-orientation
21. @hschwentner Programming 1. Learn about a domain 2. Build a model for it 3. Add technology to build the system: • programming language • UI • database • …
22. @hschwentner Coupling • thus we build coupling. we couple the system to technology • => it’s a good idea to localize that coupling! • => that’s one of the reasons for modularity
23. @hschwentner History
24. @hschwentner No Modularity goto goto Program: goto goto goto == chaos
25. @hschwentner Structured Programming Edsger Dijkstra Edgar Dijkstra: Go To Statement Considered Harmful callable unit callable unit callable unit
26. @hschwentner Information Hiding David Parnas Programming R. Morris Techniques Editor On the Criteria To Be Used in Decomposing Systems into Modules D.L. Parnas Carnegie-Mellon University This paper discusses modularization as a mechanism for improving the flexibility and comprehensibility of a system while allowing the shortening of its development time. The effectiveness of a "modularization" is dependent upon the criteria used in dividing the system into modules. A system design problem is presented and both a conventional and unconventional decomposition are described. It is shown that the unconventional decompositions have distinct advantages for the goals outlined. The criteria used in arriving at the decom- positions are discussed. The unconventional decomposi- tion, if implemented with the conventional assumption that a module consists of one or more subroutines, will be less efficient in most cases. An alternative approach to implementation which does not have this effect is sketched. Key Words and Phrases: software, modules, modularity, software engineering, KWIC index, software design CR Categories: 4.0 Introduction A lucid statement of the philosophy of modular programming can be found in a 1970 textbook on the design of system programs by Gouthier and Pont [1, ¶I0.23], which we quote below: 1 A well-defined segmentation of the project effort ensures system modularity. Each task forms a separate, distinct program module. At implementation time each module and its inputs and outputs are well-defined, there is no confusion in the intended interface with other system modules. At checkout time the in- tegrity of the module is tested independently; there are few sche- duling problems in synchronizing the completion of several tasks before checkout can begin. Finally, the system is maintained in modular fashion; system errors and deficiencies can be traced to specific system modules, thus limiting the scope of detailed error searching. Usually nothing is said about the criteria to be used in dividing the system into modules. This paper will discuss that issue and, by means of examples, suggest some criteria which can be used in decomposing a system into modules. Copyright @ 1972, Association for Computing Machinery, Inc. General permission to republish, but not for profit, all or part of this material is granted, provided that reference is made to this publication, to its date of issue, and to the fact that reprinting privileges were granted by permission of the Association for Com- puting Machinery. Author's address: Department of Computer Science, Carnegie- Mellon University, Pittsburgh, PA 15213. A Brief Status Report The major advancement in the area of modular programming has been the development of coding techniques and assemblers which (l) allow one module to be written with little knowledge of the code in another module, and (2) allow modules to be reas- sembled and replaced without reassembly of the whole system. This facility is extremely valuable for the production of large pieces of code, but the systems most often used as examples of problem systems are highly- modularized programs and make use of the techniques mentioned above. 1 Reprinted by permission of Prentice-Hall, Englewood interface imple- mentation " #
27. @hschwentner Separation of Concerns Edsger Dijkstra “…study in depth an aspect in isola,on […], all the 3me knowing that one is occupying oneself only with one of the aspects.” one aspect in isolation
28. @hschwentner Separation of Concerns • Single responsibility principle • do one thing well • Change because of one reason • Separation of business logic and technical code
29. @hschwentner Loose Coupling/ High Cohesion Ed Yourdon Larry Constantine ! in which direction?
30. @hschwentner Layered Architecture
31. @hschwentner 2 Layer Architecture Program “uses” Legend: DB
32. @hschwentner below The One Rule above Acyclic Dependency Principle allowed forbidden
33. @hschwentner Fundamental Theorem of Software Engineering David Wheeler $ “We can solve any problem by introducing an extra level of indirection” “…except for the problem of too many levels of indirection”
34. @hschwentner 3 Layer Architecture Presentation Logic Data
35. @hschwentner 4 Layer Architecture User Interface Application Domain Infrastructure
36. @hschwentner Patterns for the Domain Layer
37. @hschwentner Domain Logic Patterns Martin Fowler !
38. @hschwentner Domain Logic Patterns Martin Fowler ! • Transaction Script • Table Module • Domain Model
39. @hschwentner Rules of thumb:
40. Objects from real world turn into objects in software
42. Actions from real world turn into operations in so!ware
44. => Object-orientation
45. Values from real world turn into values in software
47. @hschwentner Domain-Driven Design Eric Evans "
48. @hschwentner Entity Tactical Design Value Object Is it a thing? Is it a property of a thing? Can you touch it? Is it identityless? Does it have an identity? Rules of Thumb
49. @hschwentner Entity vs. Value - Identity - Life cycle - Can be mutable - No identity - Always immutable Contract Map Name Length 12.5 m “John Miller” Entity Value Object
50. @hschwentner Entity Value Object Aggregate Service Factory Repository Tactical Design
51. «En$ty» BankAccount withdraw() deposit() «Value Object» Amount
52. @hschwentner The Problem with Layers
53. @hschwentner The Problem Infrastructure User Interface Application Domain allowed BAD!
54. @hschwentner The Problem Domain Infrastructure bank transaction Oracle DB Concrete BAD!
55. @hschwentner Beyond Layered Architecture
56. @hschwentner below above From above/below to inside/outside out- side inside
57. @hschwentner port port Hexagonal Architecture Foto: Dennis Hamilton/flickr/CC BY 2.0 http://alistair.cockburn.us/Hexagonal%2Barchitecture adapter adapter Alistair Cockburn
58. @hschwentner Kinds of Ports - For UI etc. - Methods to be called - “from above” - For DB and infrastructure - Interfaces to be implemented - “from below”
59. @hschwentner secondary port primary port adapter adapter Kinds of Ports Legend: Flow of control Dependency
60. @hschwentner Domain The Solution Domain Infrastructure bank transaction Oracle DB Infrastructure bank transaction Oracle DB port adapter Step 1
61. @hschwentner uses implements Legend:
62. @hschwentner Dependency Inversion Depend on abstractions, not on concretions! Robert C. Martin “Uncle Bob” "
63. @hschwentner Onion Architecture U I “application core” domain services domain model infra app ture struc serv lication ices !
64. @hschwentner The 4 Tenets •The application is built around an independent object model •Inner layers define interfaces. Outer layers implement interfaces •Direction of coupling is toward the center •All application core code can be compiled and run separate from infrastructure Jeffrey Palermo ! "
65. @hschwentner Designed for Testability “All application code can be compiled, run, and tested separate from infrastructure” Easy unit tests Plays well with TDD !
66. @hschwentner Clean Architecture Robert C. Martin “Uncle Bob” interactor = use case object U I entities DB devices w eb control use cases gate presenters lers ways
67. The price of cleanness is eternal mapping
68. Explicit Architecture Herberto Graca #
69. @hschwentner Putting it all together
70. @hschwentner Architecture Hamburger Application Domain Infrastructure UI coarse grained Henning Schwentner $
71. @hschwentner Architecture Hamburger fine grained model repository interface controller use case service entity value object view data model repository implementation widget library REST frame- work transaction handling domain library programming language ORM file system access domain event
72. @hschwentner What about Spring, JPA, Hibernate & co.?
73. @javax.persistence.Entity class BankAccount { /*...*/ } @javax.persistence.Embeddable class Amount { /*...*/ }
74. import javax.persistence.*; @Entity class BankAccount { @Id IBAN iban; @Embedded Amount balance; /*...*/ } @Embeddable class Amount { /*...*/ }
75. import javax.persistence.*; @Entity class BankAccount { @Id IBAN iban; @Embedded Amount balance; /*...*/ } When you use this You have to have this …and a default constructor …and you can’t have final fields
76. import javax.persistence.*; @Entity class BankAccount { @Id final IBAN iban; @Embedded Amount balance; /*...*/ } the identity schould never change …and it should be ini8alized at crea8on, i.e. in the constructor
77. import jakarta.persistence.*; @Entity class BankAccount { @Id final IBAN iban; @Embedded Amount balance; /*...*/ } when someone changes the technology, we have to change the business logic, too
78. @hschwentner LeasingNinja https://leasingninja.io
79. @hschwentner DEMO leasingninja-java-bigballofmud-anemicdomainmodel leasingninja-java-boundedcontext-domainmodel leasingninja-java-boundedcontext-polluteddomainmodel
80. xMolecules
81. xMolecules $ Henning Schwentner Stephan Pirnbaum Oliver Drotbohm
82. import org.jmolecules.ddd.annotation.*; @Entity class Account { @Identity public final IBAN iban; public void deposit(Amount amount) //... public void withdraw(Amount amount) //... }
83. @hschwentner Boilerplate and Model Pollution Reduction
84. @hschwentner Domain-Driven Refactorings • Strategic Refactorings • Tac3cal Refactorings (Against Big Ball of Mud) Catalog: h"ps://hschwentner.io/domain-driven-refactorings strategic transformation tactical transformation team-organizational transformation • Socio-Technical • Tac3cal refactorings (Against Model Anemia)
85. https://hschwentner.io Read on in: https://hschwentner.io/domain-driven-refactorings
87. https://hschwentner.io
89. @hschwentner FEEDBACK
92. @hschwentner Bibliography Buschmann, Frank, Regine Meunier, Hans Rohnert, Peter Sommerlad, and Michael Stal. Pattern-Oriented Software Architecture Volume 1: A System of Patterns. Hoboken, NJ: Wiley, 1996. Cockburn, Alistair. “Hexagonal Architecture.” January 4, 2005. https://alistair.cockburn.us/hexagonal-architecture/. Dijkstra, Edsger. “Go To Statement Considered Harmful.” Communications of the ACM 11, no. 3 (March 1968): 147–48. Evans, Eric. Domain-Driven Design: Tackling Complexity in the Heart of Software. Boston: Addison-Wesley, 2004. Fowler, Martin. Patterns of Enterprise Application Architecture. Boston: Addison- Wesley, 2005. Gamma, Erich, Richard Helm, Ralph Johnson, and John Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software. Reading, MA: Addison-Wesley, 1995. Graca, Herberto. “DDD, Hexagonal, Onion, Clean, CQRS, … How I Put It All Together.” November 16, 2017. https://herbertograca.com/2017/11/16/explicit-architecture-01-
94. Henning Schwentner ⌂ https://hschwentner.io in/henningschwentner hs@wps.de Kolleg:in gesucht (Deutschlandweit)