Embed Size (px)
DESCRIPTION
How can we quickly tell what an application is about? How can we quickly tell what it does? How can we distinguish business concepts from architecture clutter? How can we quickly find the code we want to change? How can we instinctively know where to add code for new features? Purely looking at unit tests is either not possible or too painful. Looking at higher-level tests can take a long time and still not give us the answers we need. For years, we have all struggled to design and structure projects that reflect the business domain. In this talk Sandro will be sharing how he designed the last application he worked on, twisting a few concepts from Domain-Driven Design, properly applying MVC, borrowing concepts from CQRS, and structuring packages in non-conventional ways. Sandro will also be touching on SOLID principles, Agile incremental design, modularisation, and testing. By iteratively modifying the project structure to better model the product requirements, he has come up with a design style that helps developers create maintainable and domain-oriented software.
Citation preview
Crafted Design
Sandro Mancuso@sandromancusohttp://leanpub.com/socra
What is this application about? What are the main concepts?
What does this application do? What are the main features?
Where do I need to change? Where do I put a new feature?
Looking from above, I can’t see what the application does or is about
Architectural and design concepts mixed with domain
Badly structured packages/namespaces
I don’t know where to start Classes and methods are too low level
Example: Layered structure
What does this application do? What is it about?
Example: Layered-domain structure
Books and Users. Cool, but what does this application do?
Example: MVC structure
Awesome. It’s a web application. So?
MVC & MVC Variations
• MVC (Smalltalk 76/80)• MVC (general concept – 1988)• Three-Tier Architecture (Presentation, Logic, Data)• MVC (Model 1/Model 2)• Model View Adapter (MVA)• Model View Presenter (MVP)• Model View ViewModel (MVVM)• Presentation-Abstraction-Control (PAC)• ….
MVC used badly
Anaemic Domain
Fat Controllers
Coupling with MVC framework
MVC & MVC Variations
They are all wrong. But they are also right. It all depends on the ‘V’iew.
Views impact MVC structureDepending on the view technology, Views and Controllers
responsibility becomes more/less coupled or blurred.
Web applications Single-page AJAX applications with stateless backend Console-based applications Desktop applications Games Mobile / tablets External systems (talking via Queues / Webservices)
However, the model should remain unchanged.
MVC – A Macro Organisational Pattern
Model
V C M
?
DeliveryMechanism
“Model” is overloaded and confusing
Model (M in MVC) Domain Model (DDD) View Model Data Model Entities & Active Record
and other artificial definitions from MVC frameworks
Associated with the persistence mechanism?
M => Domain Model (DDD)
Domain Model combines state and behaviour, with more focus on the latter.
DDD define a few building blocks to your domain:
Entities Value Objects Factories Repositories
Services Application Domain Infrastructure
Aggregates
<< Web app >>
Embedded Domain Model
ModelV C DM
DeliveryMechanism
Infrastructure Infrastructure
DBQueue
Deployable Domain Model
DeliveryMechanisms
<< external system >>
<< mobile app >>
DB
<< deployable app >>
Model
Infrastructure
DM<<W/S>>
<<W/S>>
Event-Driven Domain Model
DeliveryMechanisms DB
Queue
<< external app 2 >>
<< external app 1 >> << deployable app >>
Model
Infrastructure
DMQueue
<<event 1>>
<<event 2>>
Domain Model – Responsibilities
UC = Use Case, DS = Domain Service, S = Infra. Service, R = Repository
Model
UC 1
R 3
DS 1
DS 3
R 1
S
Infrastructure Impl
DM
DS 2
Impl
UC 2
<< web app >>
Repositories (not DAOs)
Model
<<repository>>
Library
<<repository>>
Users
Infrastructure<<Mongo>>
Books
Domain Model
<<Oracle>>
Users
“A Repository represents all objects of a certain type as a conceptual set. It acts like a collection, except with more elaborate querying capability.”
~ Eric Evans
Command & Query Use Cases
<< web app >>
Model
RDS
<<Write Model>>
UC
Model
<<Read Model>>
UC
DB
DB
Queue <<domain events>>
So, how does the app structure look like?
Web project responsibility
Control flow (invoke use cases)
JSON / XML parsers or converters
Page Objects, validators, etc
Static files
Core responsibility (simple project)
Tells what the system is about
Tells what the system does
Core responsibility (bigger project)
Epic / Theme
Epic / Theme
Epic / Theme
Related domain concepts
What is inside model packages?
Aggregate root (entity)
Repository
Entity (part of Book aggregate)
Domain Service
Value Object (part of Book aggregate)Part of aggregate behaviour
Repository
Value Object (part of User aggregate)
Aggregate root (entity)
Domain Service
What is inside infrastructure?
Interfaces defined by the domain.Dependency Inversion Principle (DIP)
CreditCardProcessor implementations
Repository implementations
Domain Model collaborations guideline
C
UC 1
UC 2
DS 1
DS 3
DS 2
R 3
R 1
cl
cl
cl
cl
C = Controller, UC = Use Case, DS = Domain Service, R = Repository, cl = class
Class responsibility
C UC DS R
cl
DB
Input Output
End of code branch
Produces the outputEnd of flow
First to handle inputStart of the flow
Execution Flow
Closer to the input: Control flow, higher level abstraction, detailed work is delegated (e.g. ProcessTrade (UC), MakePayment (UC)) — More suitable for Outside-In TDD (mockist).
Closer to the output / end of branch: Specific and detailed behaviour, no delegation, lower level abstraction (e.g. Parse XML (Parser), Create User (Repository))
Domain Model entry point Domain Concept
entry point
Defining testing strategies and boundaries
• Unit• Integration• Acceptance• Journey• Black box• Component• System• Functional• Alpha• Beta• Conformance• …
Types of tests
?
Testing strategies: User Journey
Model
UC 1
DM
UC 2
<< web app >>UC 1
UC 2
Tests the journey a user will have to do something useful in the system
Application is tested as a black box normally using a BDD framework
Use cases are facked. We just want to know if the application presents the user with the correct journey
Designed according to User Stories and Features
<<fake>>
<<fake>>
Infrastructure Impl
Testing strategies: Acceptance (Action / Behavioural)
UC DS 1
<<mock>>
RDS 2 R
Tests a behaviour (action) provided by the system
Use Case is the entry point and all external dependencies are stubbed
Domain Model
Normally tested using a BDD framework
Testing strategies: IntegrationTests the classes at the system boundaries
Infrastructure Impl
UC DS 1
<<mock>>
RDS 2 R
Domain Model
Normally done using an in-memory Database using a unit testing framework
Testing strategies: Unit (Class level)Unit test at class/method level
Infrastructure Impl
UC DS 1
RRDS 2
Domain Model
DS 1
DS 2All collaborators are mocked / stubbed (spies)
Testing strategies: End-to-End
Model
UC 1
R 3
DS 1
DS 3
R 1
S
Infrastructure Impl
DM
DS 2
Impl
UC 2
<< web app >>
Full application deployed
Uses BDD framework, accessing a testing database and fake external dependencies
Very few tests at this level, just to make sure application is wired properly
Outside-In vs. Classic TDD
The closer to the input a class is, the more flow control and delegation it does. The closer to the output a class is, the more specific and less delegation it does.
Using Outside-in TDD starting from Controllers and/or Use Cases.
Model
UC 1
R 3
DS 1
DS 3
R 1
S
Infrastructure Impl
DM
DS 2
Impl
UC 2
<< web app >>
Answering the two original questions What is the application about? (main concepts)
What does the application do? (main features)
Expressed by nouns
Expressed by verbs(Actions)
Thank You
http://leanpub.com/socra
@sandromancuso
