Clean architecture with ddd layering in php

Clean Architecture using
DDD layering in PHP
Leonardo Proietti
@_leopro_

Definition of Clean Architecture

Definition of Clean Architecture
Independent of Frameworks
Testable
Independent of UI
Independent of Database
Independent of any external agency

Hey bro, I respect your opinion but ...

Do you know "Uncle Bob", isn't it?

The Dependency Rule
“This rule says that code dependencies can
only point inwards. Nothing in an inner circle
can know anything at all about something in an
outer circle.”
(http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html)

What is Domain Driven Design?
“it is a way of thinking and a set of priorities,
aimed at accelerating software projects that
have to deal with complicated domains”
(Eric Evans, "Domain Driven Design")

“is a collection of principles and patterns that
help developers craft elegant object systems”
(http://msdn.microsoft.com/en-us/magazine/dd419654.aspx)

“is an approach to software development for
complex needs by connecting the
implementation to an evolving model”
(http://en.wikipedia.org/wiki/Domain-driven_design)

Mmhh interesting … but what does it mean?

Domain
“Every software program relates to some
activity or interest of its user. That subject area
to which the user applies the program is the
domain of the software”

Model
“A model is a simplification. It is an
interpretation of reality that abstracts the
aspects relevant to solving problem at hand
and ignores extraneous detail.”

Model
“A domain model [...] is not just the knowledge
in a domain expert’s head; it is a rigorously
organized and selective abstraction of that
knowledge.”

Next it’s maybe the most important thing in DDD

Ubiquitous Language
“the domain model can provide the backbone
for that common language [...]. The vocabulary
of that UBIQUITOUS LANGUAGE includes the
names of classes and prominent operations”

Ubiquitous Language
It’s a shared jargon between domain experts
and developers, based on Domain Model

Take care of Ubiquitous Language

What does “coffee” mean?
Alberto Brandolini AKA ziobrando

Ubiquitous Language
“changes to the language will be recognized as
changes in the domain model”

Context
“The setting in which a word or statement
appears that determines its meaning.”

Entity
An object with “clear identity and a life-cycle
with state transitions that we care about.”
(http://dddsample.sourceforge.net/characterization.html)

It depends.
“We don't assign seats on our flights,
so feel free to sit in any available seat”

Value Object
“An object that contains attributes but has no
conceptual identity. They should be treated as
immutable.”
(http://en.wikipedia.org/wiki/Domain-driven_design)

Value Object
“A small simple object, like money or a date
range, whose equality isn't based on identity.”
(http://martinfowler.com/eaaCatalog/valueObject.html)

In most of the contexts, but ...

Beware about Anemic Domain Model

Beware about Anemic Domain Model
Both Entity and Value Object
should have data and behaviours.
(http://www.martinfowler.com/bliki/AnemicDomainModel.html)

Few other concepts
Repository
Aggregate
Domain Event

Repository
“A REPOSITORY represents all objects of a
certain type as a conceptual set. It acts like a
collection, except with more elaborate querying
capability”

Repository
“All repositories provide methods that allow
client to request objects matching some
criteria”

Repository
“Although most queries return an object or a
collection of objects, it also fits within the
concept to return some types of summary
calculation”

Aggregate
“A DDD aggregate is a cluster of domain
objects that can be treated as a single unit.”
(http://martinfowler.com/bliki/DDD_Aggregate.html)

Aggregate
“DDD aggregates are domain concepts (order,
clinic visit, playlist), while collections are
generic.”
(http://martinfowler.com/bliki/DDD_Aggregate.html)

Domain Event
“Captures the memory of something interesting
which affects the domain”
(http://martinfowler.com/eaaDev/DomainEvent.html)

Layering
“We need to decouple the domain objects from
other functions of the system, so we can avoid
confusing the domain concepts wiht other
concepts”

Layering
(http://guptavikas.wordpress.com/2009/12/01/domain-driven-design-an-introduction/)

Layering
(http://dddsample.sourceforge.net/architecture.html)

Domain
“The domain layer is the heart of the software,
and this is where the interesting stuff happens.”

Application
“The application layer is responsible for driving
the workflow of the application, matching the
use cases at hand”

Interface
“This layer holds everything that interacts with
other systems”

Interface
“This layer holds everything that interacts with
other systems”
Controller Form
View API

Infrastructure
“In simple terms, the infrastructure consists of everything
that exists independently of our application: external
libraries, database engine, application server, messaging
backend and so on.”

Services
“Sometimes, it just isn’t a thing.”

Services
Domain Services
Application Services
Infrastructural Services

Domain Services
“If a SERVICE were devised to make
appropriate debits and credits for a found
transfer, that capability would belong in the
domain layer”

Application Services
“if the banking application can convert and
export our transactions into a spreadsheet file
[...] that export is an application SERVICE”

Infrastructural Services
“a bank might have an application that sends
an e-mail [...]. The interface that encapsulates
the email system, [...] is a SERVICE in the
infrastructure layer”

Persistence Ignorance
“In DDD, we don't consider any databases.
DDD is all about the domain, not about the
database, and Persistence Ignorance (PI) is a
very important aspect of DDD”
(http://williamdurand.fr/2013/08/20/ddd-with-symfony2-making-things-clear/)

YAGNI
You aren't gonna need it.
You don’t need a Database or a Framework to
modelling the Domain

DDD is Agile, we should be iterative

Our starting domain
I need a tool to plan my trips.
Every trip must have at least one route
and every route has one or more leg.
A leg has one date and one location.

Code
Here, a complete sample code:
https://github.com/leopro/trip-planner
You can follow the building steps, starting from the
first commit.

Code
Let’s focus on some steps

composer.json
{
"name": "my trip planner",
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
"doctrine/collections": "v1.2",
},
"require-dev": {
"phpunit/phpunit": "4.0.*"
},
"config": {
"bin-dir": "bin"
}
}

composer.json
{
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
},
"require-dev": {
},
"config": {
"bin-dir": "bin"
}
}
I don't need anything
more to start

composer.json
{
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
},
"require-dev": {
},
"config": {
"bin-dir": "bin"
}
}
Ok, I have a dependency on
doctrine/collections ...

composer.json
{
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
},
"require-dev": {
},
"config": {
"bin-dir": "bin"
}
}
… the missing (SPL)
Collection/Array/OrderedMap interface

composer.json
{
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.3.3",
},
"require-dev": {
},
"config": {
"bin-dir": "bin"
}
}
Anyway, you can put a boundary

<?php
namespace LeoproTripPlannerDomainContract;
use DoctrineCommonCollectionsCollection as DoctrineCollection;
interface Collection extends DoctrineCollection {}

<?php
namespace LeoproTripPlannerDomainAdapter;
use DoctrineCommonCollectionsArrayCollection as DoctrineArrayCollection;
use LeoproTripPlannerDomainContractCollection;
class ArrayCollection extends DoctrineArrayCollection implements Collection {}

<?php
namespace LeoproTripPlannerDomainTests;
use LeoproTripPlannerDomainEntityTrip;
class TripTest extends PHPUnit_Framework_TestCase
{
public function testCreateTripReturnATripWithFirstRoute()
{
$trip = Trip::create('my first planning');
$this->assertInstanceOf('LeoproTripPlannerDomainEntityTrip', $trip);
$this->assertEquals(1, $trip->getRoutes()->count());
}
}

<?php
namespace LeoproTripPlannerDomainEntity;
use LeoproTripPlannerDomainAdapterArrayCollection;
class Trip
{
private $name,
private $routes;
private function __construct($name, Route $route)
{
$this->name = $name;
$this->routes = new ArrayCollection(array($route));
}
public function create($name)
{
return new self($name, new Route);
}
public function getRoutes()
{
return $this->routes;
}
}

<?php
class Route
{
}

<?php
use LeoproTripPlannerDomainEntityRoute;
class RouteTest extends PHPUnit_Framework_TestCase
{
public function testCreateRouteAddingALeg()
{
$route = Route::create('my first trip');
$route->addLeg('06-06-2014');
$this->assertEquals(1, $route->getLegs()->count());
}

<?php
class Route
{
private $name;
private $legs;
private function __construct($name)
{
$this->legs = new ArrayCollection();
}
public static function create($tripName)
{
return new self('first route for trip: ' . $tripName);
}
public function addLeg($date)
{
$leg = Leg::create($date);
$this->legs->add($leg);
}
//...

<?php
class Route
{
private $name;
private $legs;
private function __construct($name)
{
$this->legs = new ArrayCollection();
}
public static function create($tripName)
{
return new self('first route for trip: ' . $tripName);
}
{
}
//...
Wait, we really want two legs
with the same date?

The model is changing
I need a tool to plan my trips.
Every trip must have at least one route
and every route has one or more leg
and two leg with the same date for the
same route are not allowed .
A leg has one date and one location.

/**
* @expectedException ...DateAlreadyUsedException
*/
public function testNoDuplicationDateForTheSameRoute()
{
$route = Route::create('my first trip');
$route->addLeg('06-06-2014');
$route->addLeg('06-06-2014');
}

<?php
class Route
{
//...
{
$dateAlreadyUsed = function($key, $element) use($leg) {
return $element->getDate() == $leg->getDate();
};
if ($this->legs->exists($dateAlreadyUsed)) {
throw new DateAlreadyUsedException($date . ' already used');
}
}
//...

<?php
use LeoproTripPlannerDomainEntityLeg;
class LegTest extends PHPUnit_Framework_TestCase
{
public function testCreateLegReturnsALegWithDateAndLocation()
{
$leg = Leg::create('01/01/2014', 'd/m/Y', -3.386665, 36.736908);
$this->assertInstanceOf('LeoproTripPlannerDomainEntityLeg', $leg);
$location = $leg->getLocation();
$this->assertInstanceOf('LeoproTripPlannerDomainEntityLocation', $location);
$point = $location->getPoint();
$this->assertInstanceOf('LeoproTripPlannerDomainValueObjectPoint', $point);
$this->assertEquals(-3.386665, $point->getLatitude());
$this->assertEquals(36.736908, $point->getLongitude());
}
}

<?php
use LeoproTripPlannerDomainValueObjectDate;
class Leg
{
private $date;
private $location;
private function __construct(Date $date, Location $location)
{
$this->date = $date;
$this->location = $location;
}
public static function create($date, $dateFormat, $latitude, $longitude)
{
$date = new Date($date, $dateFormat);
return new self(
$date,
Location::create($date->getFormattedDate(), $latitude, $longitude)
);
}
//..

<?php
use LeoproTripPlannerDomainValueObjectPoint;
class Location
{
private $name;
private $point;
private function __construct($name, Point $point)
{
$this->point = $point;
}
public static function create($name, $latitude, $longitude)
{
return new self($name, new Point($latitude, $longitude)
);
}
public function getPoint()
{
return $this->point;
}
}

<?php
class PointTest extends PHPUnit_Framework_TestCase
{
public function testDistance()
{
$firstPoint = new Point(-3.386665, 36.736908);
$secondPoint = new Point(-3.428112, 35.932846);
$this->assertEquals(89, $firstPoint->getCartographicDistance($secondPoint));
$this->assertEquals(98, $firstPoint->getApproximateRoadDistance($secondPoint));
}
}

<?php
class PointTest extends PHPUnit_Framework_TestCase
{
public function testDistance()
{
$firstPoint = new Point(-3.386665, 36.736908);
$secondPoint = new Point(-3.428112, 35.932846);
$this->assertEquals(89, $firstPoint->getCartographicDistance($secondPoint));
$this->assertEquals(98, $firstPoint->getApproximateRoadDistance($secondPoint));
}
}
Value Object
getCartographicDistance()
getApproximateRoadDistance()

<?php
namespace LeoproTripPlannerDomainValueObject;
class Point
{
private $latitude;
private $longitude;
public function __construct($latitude, $longitude)
{
$this->latitude = $latitude;
$this->longitude = $longitude;
}
//..
public function getApproximateRoadDistance(Point $point, $degreeApproximation = 10)
{
$distance = $this->getCartographicDistance($point);
return round($distance + $distance * ($degreeApproximation / 100));
}

public function getCartographicDistance(Point $point)
{
$earthRadius = 3958.75;
$dLat = deg2rad($point->getLatitude() - $this->latitude);
$dLng = deg2rad($point->getLongitude() - $this->longitude);
$a = sin($dLat / 2) * sin($dLat / 2) +
cos(deg2rad($this->latitude)) * cos(deg2rad($point->getLatitude())) *
sin($dLng / 2) * sin($dLng / 2);
$c = 2 * atan2(sqrt($a), sqrt(1 - $a));
$dist = $earthRadius * $c;
$meterConversion = 1.609344;
$geopointDistance = $dist * $meterConversion;
return round($geopointDistance, 0);
}

public function getCartographicDistance(Point $point)
{
$earthRadius = 3958.75;
$dLat = deg2rad($point->getLatitude() - $this->latitude);
$dLng = deg2rad($point->getLongitude() - $this->longitude);
$a = sin($dLat / 2) * sin($dLat / 2) +
cos(deg2rad($this->latitude)) * cos(deg2rad($point->getLatitude())) *
sin($dLng / 2) * sin($dLng / 2);
$c = 2 * atan2(sqrt($a), sqrt(1 - $a));
$dist = $earthRadius * $c;
$meterConversion = 1.609344;
$geopointDistance = $dist * $meterConversion;
return round($geopointDistance, 0);
}
Got the point?

<?php
namespace LeoproTripPlannerApplicationCommand;
use LeoproTripPlannerApplicationUseCaseUseCaseInterface;
class CommandHandler
{
private $useCases;
public function registerCommands(array $useCases)
{
foreach ($useCases as $useCase) {
if ($useCase instanceof UseCaseInterface) {
$this->useCases[$useCase->getManagedCommand()] = $useCase;
} else {
throw new LogicException(‘...');
}
}
}
//...

<?php
{
//...
public function execute($command)
{
try {
$commandClass = get_class($command);
if (!array_key_exists($commandClass, $this->useCases)) {
throw new LogicException($commandClass . ' is not a managed command');
}
$this->useCases[get_class($command)]->run($command);
} catch (Exception $e) {
throw $e;
}
}
}

<?php
{
//...
public function execute($command)
{
try {
$commandClass = get_class($command);
if (!array_key_exists($commandClass, $this->useCases)) {
throw new LogicException($commandClass . ' is not a managed command');
}
$this->useCases[get_class($command)]->run($command);
} catch (Exception $e) {
throw $e;
}
}
}
You can move the state of the
domain, through commands

<?php
use LeoproTripPlannerApplicationContractCommandInterface;
class CreateTripCommand implements CommandInterface
{
private $name;
public function __construct($name)
{
}
public function getRequest()
{
return new ArrayCollection(
array(
'name' => $this->name
)
);
}
}

<?php
namespace LeoproTripPlannerApplicationUseCase;
class CreateTripUseCase extends AbstractUseCase implements UseCaseInterface
{
private $tripRepository;
public function __construct(TripRepository $tripRepository)
{
$this->tripRepository = $tripRepository;
}
public function run(CommandInterface $command)
{
$this->exceptionIfCommandNotManaged($command);
$request = $command->getRequest();
$trip = Trip::createWithFirstRoute(new TripIdentity(uniqid()), $request->get('name'));
$this->tripRepository->add($trip);
return $trip;
}
}

<?php
namespace LeoproTripPlannerApplicationUseCase;
class CreateTripUseCase extends AbstractUseCase implements UseCaseInterface
{
private $tripRepository;
public function __construct(TripRepository $tripRepository)
{
$this->tripRepository = $tripRepository;
}
public function run(CommandInterface $command)
{
$this->exceptionIfCommandNotManaged($command);
$request = $command->getRequest();
$trip = Trip::createWithFirstRoute(new TripIdentity(uniqid()), $request->get('name'));
$this->tripRepository->add($trip);
return $trip;
}
}
Defining a TripRepository
interface ...

<?php
use LeoproTripPlannerDomainValueObjectTripIdentity;
interface TripRepository
{
/**
* @param TripIdentity $identity
* @return LeoproTripPlannerDomainEntityTrip
*/
public function get(TripIdentity $identity);
/**
* @param Trip $trip
* @return void
*/
public function add(Trip $trip);
}

<?php
use LeoproTripPlannerDomainValueObjectTripIdentity;
interface TripRepository
{
/**
* @param TripIdentity $identity
* @return LeoproTripPlannerDomainEntityTrip
*/
public function get(TripIdentity $identity);
/**
* @param Trip $trip
* @return void
*/
public function add(Trip $trip);
}
… and interfaces for Validator
and Event Dispatcher

<?php
namespace LeoproTripPlannerApplicationContract;
interface Validator
{
/**
* @param $value
* @return LeoproTripPlannerDomainContractCollection
*/
public function validate($value);
}
interface EventDispatcher
{
/**
* @param array $listeners
* @return EventListener[]
*/
public function registerListeners(array $listeners);
/**
* @param $event
*/
public function notify($name, $event);
}

About validation
In DDD, entities should be always
valid.

About validation
But if you ask
“where do I put validation?”
you'll get different answers.

About validation
If you are using commands,
validate the command itself, is a
good trade-off.

composer.json
"require": {
"php": ">=5.3.3",
"symfony/symfony": "~2.4",
"doctrine/dbal": "dev-master",
"doctrine/orm": "dev-master",
"doctrine/doctrine-bundle": "dev-master",
"twig/extensions": "~1.0",
"symfony/assetic-bundle": "~2.3",
"symfony/swiftmailer-bundle": "~2.3",
"symfony/monolog-bundle": "~2.4",
"sensio/distribution-bundle": "~2.3",
"sensio/framework-extra-bundle": "~3.0",
"sensio/generator-bundle": "~2.3",
"incenteev/composer-parameter-handler": "~2.0",
"doctrine/data-fixtures": "dev-master",
"doctrine/migrations": "dev-master",
"doctrine/doctrine-migrations-bundle": "dev-master",
"doctrine/doctrine-fixtures-bundle": "dev-master"
},

app/config/config.yml
orm:
auto_generate_proxy_classes: "%kernel.debug%"
auto_mapping: false
mappings:
TripPlannerDomain:
type: yml
prefix: LeoproTripPlannerDomainEntity
dir: %kernel.root_dir%/../src/Leopro/TripPlanner/InfrastructureBundle/Resources/config/doctrine/entity
is_bundle: false
TripPlannerDomainValueObjects:
type: yml
prefix: LeoproTripPlannerDomainValueObject
dir: %kernel.root_dir%/../src/Leopro/TripPlanner/InfrastructureBundle/Resources/config/doctrine/value_object
is_bundle: false

InfrastructureBundle/Resources/config/entity/Route.orm.yml
LeoproTripPlannerDomainEntityTrip:
type: entity
table: trip
embedded:
identity:
class: LeoproTripPlannerDomainValueObjectTripIdentity
fields:
name:
type: string
length: 250
manyToMany:
routes:
targetEntity: LeoproTripPlannerDomainEntityRoute
joinTable:
name: trip_routes
joinColumns:
link_id:
referencedColumnName: identity_id
inverseJoinColumns:
report_id:
referencedColumnName: internalIdentity
cascade: ["persist"]

InfrastructureBundle/Resources/config/validation.yml
LeoproTripPlannerApplicationCommandCreateTripCommand:
properties:
name:
- NotBlank: ~
LeoproTripPlannerApplicationCommandAddLegToRouteCommand:
properties:
tripIdentity:
- NotBlank: ~
routeIdentity:
- NotBlank: ~
date:
- NotBlank: ~
dateFormat:
- NotBlank: ~
latitude:
- NotBlank: ~
longitude:
- NotBlank: ~

src/LeoPro/TripPlanner/InfrastructureBundle/Resources/config/services.xml
<services>

<service id="trip_repository" alias="trip_repository.doctrine"></service>
<service id="command_handler" class="%application.command_handler.class%">
<argument type="service" id="infrastructure.validator"/>
<argument type="service" id="application.event_dispatcher"/>
</service>
</services>

Adapter
Ops … some parts of the
frameworks do not fit our
interfaces.

<?php
namespace LeoproTripPlannerInfrastructureBundleAdapter;
use LeoproTripPlannerApplicationContractValidator as ApplicationValidatorInterface;
use SymfonyComponentValidatorValidatorValidatorInterface;
class Validator implements ApplicationValidatorInterface
{
private $validator;
public function __construct(ValidatorInterface $validator)
{
$this->validator = $validator;
}
public function validate($value)
{
$applicationErrors = new ArrayCollection();
$errors = $this->validator->validate($value);
foreach ($errors as $error) {
$applicationErrors->set($error->getPropertyPath(), $error->getMessage());
}
return $applicationErrors;
}
}

<?php
namespace LeoproTripPlannerInfrastructureBundleRepository;
use DoctrineORMEntityManager;
use LeoproTripPlannerDomainContractTripRepository as TripRepositoryInterface;
class TripRepository implements TripRepositoryInterface
{
private $em;
public function __construct(EntityManager $em)
{
$this->em = $em;
}
public function get(TripIdentity $identity)
{
$qb = $this->em->createQueryBuilder()
->select('t')
->from("TripPlannerDomain:Trip", 't')
->where('t.identity.id = :identity');
$qb->setParameter('identity', $identity);
return $qb->getQuery()->getOneOrNullResult();
}

<?php
{
public function add(Trip $trip)
{
$this->em->persist($trip);
$this->em->flush();
}
}

<?php
{
{
$this->em->flush();
}
}
Then it’s like a Doctrine
repository?!?

<?php
{
{
$this->em->flush();
}
}
No, it’s quite different

<?php
{
private $myThirdPartApiClient;
public function __construct(ApiClient $myThirdPartApiClient)
{
$this->myThirdPartApiClient = $myThirdPartApiClient;
}
{
$this->myThirdPartApiClient->get($identity);
}
{
$this->myThirdPartApiClient->store($trip);
}

<?php
{
private $myThirdPartApiClient;
public function __construct(ApiClient $myThirdPartApiClient)
{
$this->myThirdPartApiClient = $myThirdPartApiClient;
}
{
$this->myThirdPartApiClient->get($identity);
}
{
$this->myThirdPartApiClient->store($trip);
}
It’s another possible Repository
implementation

<?php
namespace LeoproTripPlannerPresentationBundleController;
use LeoproTripPlannerPresentationBundleFormTypeCreateTripType;
class ApiController extends Controller
{
/**
* @Route("/", name="create_trip")
* @Template
*/
public function createTripAction(Request $request)
{
$form = $this->createForm(new CreateTripType());
$form->handleRequest($request);
if ($form->isValid()) {
$trip = $this->get('command_handler')->execute($form->getData());
return new Response('ok');
}
return array(
'form' => $form->createView(),
);
}
}

<?php
namespace LeoproTripPlannerPresentationBundleFormType;
use LeoproTripPlannerApplicationCommandCreateTripCommand;
class CreateTripType extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('name')
->add('save', 'submit');
}
public function setDefaultOptions(OptionsResolverInterface $resolver)
{
$resolver->setDefaults(array(
'data_class' => 'LeoproTripPlannerApplicationCommandCreateTripCommand',
'empty_data' => function (FormInterface $form) {
$command = new CreateTripCommand(
$form->get('name')->getData()
);
return $command;
},
));
}
}

A clean architecture helps in avoiding the Big Ball of Mud.

Also starting with a very simple domain

If our system is tightly coupled

we are losing the chance of responding to changes.

… independence from frameworks, database, UI ...

… means talking about business.

Let the code speak the language of the business

First, taking care of the model

We reached the finish line, well done.

Credits
● Eric Evans, - "Domain Driven Design"
● “Uncle Bob” - http://blog.8thlight.com/uncle-bob/archive.html and books
● http://williamdurand.fr/2013/08/20/ddd-with-symfony2-making-things-clear/
● http://williamdurand.fr/2013/08/07/ddd-with-symfony2-folder-structure-and-
code-first/
● http://verraes.net/2013/04/decoupling-symfony2-forms-from-entities/
● http://www.whitewashing.
de/2012/08/22/building_an_object_model__no_setters_allowed.html
● http://nicolopignatelli.me/valueobjects-a-php-immutable-class-library/
● http://welcometothebundle.com/domain-driven-design-and-symfony-for-
simple-app/
● http://www.slideshare.net/SteveRhoades2/implementing-ddd-concepts-in-
php

Credits
● http://devlicio.us/blogs/casey/archive/2009/02/16/ddd-aggregates-and-
aggregate-roots.aspx
● http://www.slideshare.net/perprogramming/application-layer-33335917
● http://lostechies.com/jimmybogard/2008/08/21/services-in-domain-driven-
design/
● http://gorodinski.com/blog/2012/04/14/services-in-domain-driven-design-
ddd/
● http://www.slideshare.net/jeppec/agile-ddd-cqrs
● http://www.slideshare.net/thinkddd/practical-domain-driven-design-cqrs-
and-messaging-architectures
● http://www.codeproject.com/Articles/339725/Domain-Driven-Design-Clear-
Your-Concepts-Before-Yo
● http://lostechies.com/jimmybogard/2008/05/21/entities-value-objects-
aggregates-and-roots/

Credits
● http://www.slideshare.net/ziobrando/gestire-la-complessit-con-domain-
driven-design
● http://lostechies.com/jimmybogard/2009/02/15/validation-in-a-ddd-world/
● http://lostechies.com/jimmybogard/2009/09/03/ddd-repository-
implementation-patterns/
● http://www.sapiensworks.com/blog/post/2012/04/18/DDD-Aggregates-
And-Aggregates-Root-Explained.aspx
● http://www.udidahan.com/2009/06/29/dont-create-aggregate-roots/
● http://jblewitt.com/blog/?p=241
● http://www.sapiensworks.com/blog/post/2013/10/18/Modelling-Aggregate-
Roots-Relationships.aspx
● http://www.sapiensworks.com/blog/post/2013/01/15/Domain-Driven-
Design-Aggregate-Root-Modelling-Fallacy.aspx

Credits
● http://lostechies.com/jamesgregory/2009/05/09/entity-interface-anti-pattern
● http://www.slideshare.net/piotrpelczar/cqrs-28299581
● http://richarddingwall.name/2009/10/13/life-inside-an-aggregate-root-part-
1/
● http://lostechies.com/jimmybogard/2010/02/24/strengthening-your-domain-
aggregate-construction/
● http://guptavikas.wordpress.com/2009/12/21/domain-driven-design-
creating-domain-objects/
● http://gorodinski.com/blog/2012/05/19/validation-in-domain-driven-design-
ddd/
● http://verraes.net/2013/12/related-entities-vs-child-entities/
● http://devlicio.us/blogs/casey/archive/2009/02/20/ddd-the-repository-
pattern.aspx
● http://gojko.net/2009/09/30/ddd-and-relational-databases-the-value-object-
dilemma/

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