Domain-centric? Why Hexagonal, Onion, and Clean Architecture Are Answers to the Wrong Question

To separate technical from domain code, architectural approaches like Hexagonal or Onion Architecture are currently all the rage. However, discussions about their semantic details and their mapping to the source code structure of software projects are at least equally ubiquitous.

How much abstraction and mapping between architectural concepts is needed? Is persistence metadata in the domain model heresy? Above all: what is the actual goal of the exercise, and: does it have to be so complicated?

We address these and other questions in a theoretical overview and by looking at concrete examples. We discuss the trade-offs of different approaches and how various tools and libraries help us to maintain the intended structural integrity.

Transcript

1. DOMAIN-CENTRIC? WHY HEXAGONAL, ONION, AND CLEAN ARCHITECTURE ARE ANSWERS TO THE WRONG QUESTION — AND WHAT TO ASK INSTEAD Oliver Drotbohm ✉ info@odrotbohm.de    odrotbohm
3. Complexity …while the actual challenge is this. Most teams focus on that… 1.0 1.2 1.1 2.0
4. Cost of Software  Cost of Change Beck - A Daily Practice of Empirical Software Design — https://www.youtube.com/watch?v=yBEcq23OgB4 (2023) Yourdon, Constantine - Structured Design — Fundamentals of a Discipline of Computer Program and Systems Design (1979)
5. Cost of Change  Coupling
6. Change starts here…
7. Change starts here…
8. Not all coupling is born equal
9. Decoupling has its cost, too
10. Cohesion
11. Cohesion is coupling in the right™ places
12. Software design is the act of modeling units of strong cohesion, loosely coupled to each other.
15. Change starts here…
16. https://chaos.social/@odrotbohm/113826340530554922
17. "A system is never the sum of its parts, it's the product of their interactions." — Russel L. Ackoff
20. Separation of Concerns Architectures
21. Hexagonal Architecture 2005
22. Messaging 3rd party API Database HTTP / REST Adapters Application Core Port Port Port Port Port 📂 Adapter   
23. Onion Architecture 2008
24. Infrastructure Application Domain
25. Infrastructure Application Domain   ✉ 
26. Presentation Business Logic Persistence Layered Architecture Hexagonal- / Onion- Architecture
27. Business Logic Presentation Business Logic Persistence Adapter / Infrastructure Adapter / Infrastructure Layered Architecture Hexagonal- / Onion- Architecture
28. Business Logic Presentation Business Logic Persistence Adapter / Infrastructure Adapter / Infrastructure Layered Architecture Hexagonal- / Onion- Architecture
29. Controller Service Repository Layered Hexagonal Onion Presentation → Business → Persistence Driving Adapter → ← Driven Adapter Port ← Application → Port Infrastructure → ← Infrastructure Application / Domain Spring DI DI
30. Goals & Effects
31. Testability
32. Technology-Free Domain
33. Domain Centric?
34.   ✉  Application Domain Infrastructure
35.   ✉  Application Domain Infrastructure
36.       ✉  ✉  ✉  Infrastructure Infrastructure Domain Domain Domain Application Application Application Infrastructure
37.         ✉  ✉  ✉    Infrastructure Infrastructure Domain Domain Domain Application Application Application Infrastructure
38. Module Module Module         ✉  ✉  ✉    https://odrotbohm.de/2023/07/sliced-onion-architecture
39. Code structure Severely inspired by Simon Brown's https://static.simonbrown.je/modular-monoliths.pdf
40. Drotbohm
41. app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository Classic Layers Refers to Implements Legend Interface Class Package / Build Module
42. app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository Classic Layers CustomerController CustomerService CustomerServiceImpl CustomerRepository JdbcCustomerRepository Low cohesion! !
43. Classic Layers app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.service OrderService OrderServiceImpl app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository
44. app.domain app.persistence JdbcOrderRepository Classic Layers Hexagonal / Onion OrderService OrderServiceImpl OrderRepository app.web OrderController app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository
45. app.domain app.persistence Classic Layers Hexagonal / Onion app.web JdbcOrderRepository OrderService OrderServiceImpl OrderRepository OrderController app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository CustomerController CustomerService CustomerServiceImpl CustomerRepository JdbcCustomerRepository Low cohesion, too! !
46. app.domain app.persistence app.web Classic Layers Hexagonal / Onion app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository JdbcOrderRepository OrderService OrderServiceImpl OrderRepository OrderController
47. app.domain app.persistence app.web Classic Layers Hexagonal / Onion app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository Modular app.web app.service app.persistence OrderController OrderService OrderServiceImpl OrderRepository JdbcOrderRepository JdbcOrderRepository OrderService OrderServiceImpl OrderRepository OrderController
48. Classic Layers Hexagonal / Onion Modular app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository
49. Classic Layers Hexagonal / Onion Modular app.customer CustomerService CustomerServiceImpl CustomerRepository CustomerController JdbcCustomerRepository app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository
50. app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository Classic Layers Hexagonal / Onion Modular app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository app.customer CustomerService CustomerServiceImpl CustomerRepository CustomerController JdbcCustomerRepository
51. Classic Layers Hexagonal / Onion    ✉   Infrastructure Domain Application Modular app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository
52. Module    ✉   Classic Layers Hexagonal / Onion Modular app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository
53. app.customer OrderController JdbcOperations " # Classic Layers Hexagonal / Onion Modular Avoid internal complexity if domain permits app.web OrderController app.service OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.domain OrderService OrderServiceImpl app.persistence OrderRepository JdbcOrderRepository app.web OrderController app.orders OrderService OrderServiceImpl OrderRepository OrderController JdbcOrderRepository
55. https://chaos.social/@odrotbohm/113193662068876374
56. Strategic considerations
57. Functional Decomposition over Technical Decomposition
58. Intrinsic Complexity determines Accidental Complexity
59. Encapsulation over Organisation
60. One more thing…
61. $ VSCode jMolecules
62. Thank you! Oliver Drotbohm ✉ info@odrotbohm.de    odrotbohm