Clean Architecture
A Craftsman's Guide to Software Structure and Design
Connection
Split the group in 4 :
Ask this question
What characteristics do these architectures have in common? - 5'
Craft as many post-its as they can
Review what has been produced
Hexagonal architecture
Onion architecture
Concepts
Hexagonal Architecture
Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from its eventual run-time devices and databases.
Source : https://blog.octo.com/architecture-hexagonale-trois-principes-et-un-exemple-dimplementation/
Onion Architecture
Layers
Domain Model layer, where our entities and classes closely related to them e.g. value objects reside
Domain Services layer, where domain-defined processes reside
Application Services layer, where application-specific logic i.e. our use cases reside
Outer layer, which keeps peripheral concerns like UI, databases or tests
Dependency Inversion Principle (at Architecture Level)
This means that when writing our high-level business logic, we don’t want to depend directly on low-level stuff like databases, file systems, network connections, provider contracts, and such.
Instead, we should expose an abstraction that represents a higher-level business need and implements it using these low-level mechanisms.
What characteristics do these architectures have in common?
Here is some answers to the connection question :
Independent of frameworks
Does not depend on the existence of libraries
Allow us to use frameworks as tools (not a constraint)
Independent of the front-end
Can easily change the UI (from web to console)
Independent of the database
Business rules not bound to Database logic
Independent of any external agency
Business rules don’t know anything about outside world
Business rules can be tested without external components
Use Case Driven Approach
Ivar Jacobson in his book below explained we should map 1 Business Use case / 1 Application Use case. We should implement Application Use Case with the BCE "pattern" : Boundary Controller Entity :
Clean Architecture
The Clean Architecture as expressed by Robert C. Martin is a mix of the 3 architecture ideas explained before :
Entities (Enterprise business rules)
Encapsulate Enterprise wide business rules
Can be
Object with methods
Set of data structures and functions
Could be used by many different applications in the enterprise.
Use cases (Application business rules)
Capture business rules
Structure should indicate what the application is, not how it does it
Application specific business rules
Interface adapters
Set of adapters
Convert data from the format most convenient for the use cases and entities
To the format most convenient for some external agency such as the Database or the Web
In a MVC architecture : Presenters, Views, and Controllers
Frameworks & drivers
Frameworks and tools such as
Database
Web Framework
Glue code that communicates to the next circle inwards.
This layer is where all the details go
Keep these things on the outside where they can do little harm
The dependency rule
Source code dependencies can only point inwards.
Concrete Practice
Clone the repository at : https://github.com/ivanpaulovich/clean-architecture-kata-dojo
Checkout the branch “kata-initial”
Objective
Learn and practice the concepts behind Clean Architecture
Part 1
Each participant :
Position projects on the Clean Architecture Diagram
Draw the sequence diagram of the Register Use Case
Correction
Part 2
Cover the following use cases and requirements:
The customer can register a new account.
Allow to get the customer details.
Allow to get the account details.
Allow to deposit into an existing account.
Allow to withdraw from an existing account.
Accounts can be closed only if they have zero balance.
Accounts does not allow to withdraw more than the current account balance.
You can check in the branch final-solution to see one possible implementation of those Use Cases
Conclusion
What benefits do you see?
Pros and cons ?
Pros & Cons
Pros | Cons |
Plays well with DDD – architecture that builds everything on top of a domain model | Learning curve – People tend to mess up splitting responsibilities between layers, especially harming the domain model |
Directed coupling – the most important code in our application depends on nothing, everything depends on it | Indirection – interfaces everywhere! |
Flexibility – from an inner-layer perspective, you can swap out anything in any of the outer layers and things should work just fine | Potentially heavy |
Testability – since your application core does not depend on anything else, it can be easily and quickly tested in isolation |
Support
Resources
Hexagonal Architecture : https://blog.octo.com/architecture-hexagonale-trois-principes-et-un-exemple-dimplementation/
Onion Architecture : https://bitbucket.org/jeffreypalermo/onion-architecture/src
Clean Architecture : https://blog.cleancoder.com/uncle-bob/2012/08/13/the-clean-architecture.html
A simple template for Onion Architecture with .NET 5 : https://pereiren.medium.com/a-simple-template-for-onion-architecture-with-net-5-6c0e2f3b29c8
Last updated