Clean Architecture

Based on Mathew Renze's Pluralsight course (2016): https://app.pluralsight.com/library/courses/clean-architecture-patterns-practices-principles/

Source Code: https://github.com/matthewrenze/clean-architecture-demo

and Ardalis: https://www.youtube.com/watch?v=tYoqmL6e4oY

See also

https://github.com/boeschenstein/ddd

Classic 3 Layer

stateDiagram-v2

    state UI {

        state Business-Logic {

            state Data-Access {

                Database
            }
        }
    }

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Domain Centric approaches

• Hexagonal: https://alistair.cockburn.us/hexagonal-architecture/
• Onion: https://jeffreypalermo.com/2008/07/the-onion-architecture-part-2/
• Clean: https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html
• Comparison aka it's all the same: https://blog.ploeh.dk/2013/12/03/layers-onions-ports-adapters-its-all-the-same/

Application Layer

Overview

Interfaces

CQS - Command and Query Separation

• Commands: change data (sideeffects)
• Queries: no data change allowed (idempotent)
• Where to use? everywhere: API, services, ...
• Theory: https://martinfowler.com/bliki/CommandQuerySeparation.html
• Examples: https://khalilstemmler.com/articles/oop-design-principles/command-query-separation/
• Wikipedia: https://en.wikipedia.org/wiki/Command%E2%80%93query_separation

CQS in Database Access - Variants

• Single DB CQS
• 2 DB CQS
• Event Sourcing CQS

Unit Testing

https://github.com/boeschenstein/testing/tree/main

Layers

Layer	Level	Short	Other Names	Function	Hints
L4	low	Frameworks & Drivers	Web, UI, DB, Devices, External Interfaces, ServiceHost		not much code
L3		Interface Adapters	Controller, Gateway, Presenter	Data Conversion, Formatting
L2		Use Cases	Interactors	Application Business Rules	Services
L1	high	Entities	Domain	Enterprise Business Rules	most stable (changes rarely)

• If you need more layers: add it
• Cross-Cutting concerns: across all layers
• use Dependency Inversion for external devices (DB, ...)

Examples

Each line is a C# project:

Example 1:
	L4 Tests
	L4 Presentation
	L4 Persistence, Infrastructure
	L2+L3 Application
	L1 Entities: Domain

Example 2:
	L4 CLI
	L4 IO
	L1+L2+L3 Core

Example 3:
	L4 Tests
	L4 Frontend, Presentation UI, Web
	L4 Infrastructure, Persistance, IO
	L2+L3 Domain.Services
	L1 Entities: Domain

Example 4:
	L4 Tests
	L4 Frontend, Presentation UI, Web
	L4 Infrastructure, Persistance, IO
	L4 Hangfire (ServiceHost)
	L3 Application Services
	L2 Domain Services
	L1 Entities, Domain, DomainModel

UML

UML Class Diagram https://en.wikipedia.org/wiki/Class_diagram

Source Code Dependencies:

-->  Open arrowheads are using relationships. 
-|>  Closed arrowheads are implements or inheritance relationships. "Dependency Inversion"

Report Generator -> Data Service <|- Repository -> Database

Create Solution

dotnet new classlib --name MyApp.MyDomain

dotnet new classlib --name MyApp.MyDomain.MyServices
dotnet add MyApp.MyDomain.MyServices reference MyApp.MyDomain

dotnet new classlib --name MyApp.Infrastructure.MyDB
# Dependency Inversion: see Domain centric architectures (Clean Architecture, DDD and others)
dotnet add MyApp.Infrastructure.MyDB reference MyApp.MyDomain.MyServices

dotnet new webapi --name MyApp.MyWebApi
dotnet add MyApp.MyWebApi reference MyApp.MyDomain.MyServices
dotnet add MyApp.MyWebApi reference MyApp.Infrastructure.MyDB

# Test project
dotnet new xunit --name MyApp.MyTest
dotnet add MyApp.MyTest reference MyApp.MyDomain.MyServices
dotnet add MyApp.MyTest reference MyApp.Infrastructure.MyDB
dotnet add MyApp.MyTest reference MyApp.MyWebApi
# dotnet add MyApp.MyTest package xUnit
dotnet add MyApp.MyTest package Moq

# Solution
dotnet new sln --name MyApp
dotnet sln add MyApp.MyDomain
dotnet sln add MyApp.MyDomain.MyServices
dotnet sln add MyApp.Infrastructure.MyDB
dotnet sln add MyApp.MyWebApi
dotnet sln add MyApp.MyTest

# ADD NEW ANGULAR PROJECT
# 1) Create new Project, using "Standalone TypeScript Angular Template" in Visual Studio, add it (manually) to sln
# 2) port of 'target' in MyAngularApp\src\proxy.conf.js must be equal to port of https entry of MyWebApi in MyWebApi\Properties\launchSettings.json
# Details: https://learn.microsoft.com/en-us/visualstudio/javascript/tutorial-asp-net-core-with-angular?view=vs-2022

Information

• Screaming Architecture: https://levelup.gitconnected.com/what-is-screaming-architecture-f7c327af9bb2
• Last Responsible Moment (LRM: wait as long as you can)
• Evolutionary Architecture
• Books
  • Martin Fowler: Patterns of Enterprise Application Architecture
  • Uncle Bob: Clean Architecture
• Web
  • Martin Fowler: https://martinfowler.com
  • Udi Dahan: https://udidahan.com