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ADVANCED APPLICATION
ARCHITECTUREI - Layers
Matthias Noback @matthiasnoback
matthiasnoback/ layers-ports-and-adapters-
workshopClone from GitHub
docker-compose pull
bin/composer.sh install
docker-compose up -d
ARCHITECTUREDecisions about coupling and cohesion
COUPLINGHow are things linked to each other?
COHESIONWhich things belong together?
LAYERED ARCHITECTUREAn answer to both questions
LAYERSHelp you protect what's in a deeper layer
LAYERSAllow you to define dependency rules
LAYERSDefine the right place to put things
TRADITIONAL LAYERING
view model
data
LAYERSHorizontal division (as opposed to...)
USE CASESVertical division
LAYERSRendered as circles
CLEAN ARCHITECTUREOr "union" architecture
COHESIONA basic set of layers
infrastructure application
domain
COUPLINGThe dependency rule
Layers should only depend on deeper layers
COUPLINGDependency inversion principle
Classes should always depend on things that are more abstract
COUPLINGDependency inversion principle
low-levelconcrete class specific
abstract interface generic high-level
COUPLINGDependency inversion principle
use
COUPLINGDependency inversion principle
use implement
COUPLINGIs about dependencies in code
Use Dependency Injection
LAYER CONVENTIONSDomain layer
Domain model:
➤ Entities
➤ Value objects
➤ Domain services
➤ Factories
Business logic
Decisions
Data
State
Behavior
LAYER CONVENTIONSApplication layer
➤ Find an object
➤ Change something
➤ Notify something
➤ Get some information
Use cases
Orchestration
LAYER CONVENTIONSInfrastructure layer
Communication with:
➤ HTTP client
➤ Database
➤ Filesystem
➤ Email server
➤ Message broker
Connecting the application to
the world outside
MATTHIASNOBACK/LAYERS-PORTS-AND-ADAPTERS-
WORKSHOPAssignments are on GitHub in assignments/
assignment/01.mdLayers
ADVANCED APPLICATION
ARCHITECTUREII - Ports & adapters
MESSAGING... is the big idea
PORTS (COHESION)Web, CLI, test client, messages, database queries
User interface
Persistence
PORTS... AND ADAPTERSTranslation
HTTP
SQL
HEXAGONAL ARCHITECTURESame thing!
User interface
Persistence
PORTS... AND ADAPTERS(De)serialization, translation, structural validation
HTTP
SQL
!
!
assignment/02.mdPorts
PORT ADAPTERS...in the Infrastructure layer
APPLICATION SERVICES... in the Application layer
DOMAIN MODELin the Domain layer
APPLICATION SERVICESDelivery-mechanism agnostic
assignment/03.mdInput adapters
VALIDATIONAt different levels
Structural validation of messages
User-friendly input validation
Domain invariant protection
assignment/04.mdInput validation
APPLICATION SERVICESTransactional consistency
assignment/05.mdOutput adapter
assignment/06.mdA hidden dependency on the persistence mechanism
ADVANTAGES OF USING LAYERS, PORTS & ADAPTERS
Offers insight into the application
Isolates the low-level details
Allows for alternative implementations
Helps with testing
ADVANCED APPLICATION
ARCHITECTUREIII - Testing
UNIT TESTSTesting your units of code
One class at a time
No IO
No setup required
Mocking only dependencies "you own"
INTEGRATION TESTSTesting your adapters
Maybe multiple classes
Including IO
Some setup required
Mocking no dependencies
ACCEPTANCE TESTSTesting your application services
Multiple classes
Use cases
Infrastructure stand-ins
SYSTEM TESTSTesting your application end-to-end
The real deal
TESTING PYRAMIDMake it well-balanced
Unit
Integration
System
Acceptance
assignment/07.mdDifferent types of tests
ACCEPTANCE TESTSUse infrastructure stand-ins
Acceptance testtest the
application layer
Persistence
FileBased InMemory
Port
Adapters
MeetupRepository
FileBasedMeetupRepository InMemoryMeetupRepository
Domain
Infrastructure
implements implements
assignment/08.mdA test double for the Persistence port
assignment/09.md An acceptance test for the application layer
A WELL-BALANCED TEST SUITE
Adapters can be easily replaced
Test suite is fast
Feedback is quick
Small amount of fragile tests
Enables continuous delivery
assignment/10.mdNotifications
https://training.matthiasnoback.nl/
