PRDCW-avent-aggregator

AMIR BARYLKO
DECOUPLING
WITH THE
EVENT AGGREGATOR

WHO AM I?

• Quality Expert

• Architect

• Developer

• Mentor

• Great cook

• The one who’s entertaining you for the next hour!
Amir Barylko - Event Aggregator MavenThought Inc.

RESOURCES

• Email: amir@barylko.com

• Twitter: @abarylko

• Blog: http://www.orthocoders.com

• Materials: http://www.orthocoders.com/presentations


INTRO
Coupling
Cohesion
Dependencies
Dependency Injection
IoC Containers


COUPLING & COHESION


COUPLING
(WIKIPEDIA)

Degree to which
each program module relies
on each one
of the other modules


COUPLING II

Is usually contrasted
with cohesion


COUPLING III

Invented by Larry Constantine,
an original developer of
Structured Design


COUPLING IV

Low coupling is often a
sign of a well-structured
computer system and a
good design


COUPLING V

When combined with
high cohesion,
supports high
readability and
maintainability

COHESION
(WIKIPEDIA)

measure of how
strongly-related the
functionality expressed by the
source code of a
software module is

IS ALL ABOUT
DEPENDENCIES


HARDCODED
DEPENDENCIES
public MovieLibrary()
{
this._storage = new LocalStorage();

this._critic = new JaySherman();

this._posterService = new IMDBPosterService();
}

very hard to test
and maintain!


EXTRACT INTERFACES
private JaySherman _critic;

private IMDBPosterService _posterService;

private LocalStorage _storage;

private IMovieCritic _critic;

private IMoviePosterService _posterService;

private IMovieStorage _storage;


DEPENDENCY INJECTION
public MovieLibrary(IMovieStorage storage,
IMovieCritic critic,
IMoviePosterService posterService)
{
this._storage = storage;
this._critic = critic;
this._posterService = posterService;
}

Better for testing... but who
is going to initialize them?


INVERSION OF CONTROL


POOR’S MAN DI
public MovieLibrary()
{
this._storage = new LocalStorage();

this._critic = new JaySherman();

this._posterService = new IMDBPosterService();

}

Still testeable...
but smells!


USING IOC CONTAINER
Container.Register(
Component
.For<IMovieCritic>()
.ImplementedBy<JaySherman>(),
Component
.For<IMoviePosterService>()
.ImplementedBy<IMDBPosterService>(),
Component
.For<IMovieStorage>()
.ImplementedBy<LocalStorage>());


REFACTORING
What’s wrong?
Event Aggregator
Demo
Desktop &Web applications


WHAT’S WRONG?


TOO MANY DEPENDENCIES


LET’S THINK

• Why the critic has to know the library (or
viceversa)?

• Or the poster service?
• If I need more services, do I add more
dependencies to the library?


DECENTRALIZE

• Identify boundaries
• Identify clear responsibilities
• Reduce complexity
• Find notiﬁcation mechanism


WHAT I’D LIKE

Reviews

Library ????

Posters


EVENT AGGREGATOR


THE PATTERN

Channel events
from multiple
objects into a
single object to
s i m p l i f y
registration for
clients

TRAITS

• Based on subject - observer
• Centralize event registration logic
• No need to track multiple objects
• Level of indirection


IMPLEMENTATION


WHAT WE NEED

•Register events
•Raise events
•Subscribe to events


ATTEMPT #1


ATTEMPT #2


WHAT?
NO CONCRETE EVENT?
• How can we get a concrete from an interface?

• Castle Dynamic Proxy!

•I have an interface and get a Proxy to a stub

• All properties are stubbed to be conﬁgured!


RAISING AN EVENT


HOW TO USE IT

if( !everybody.Asleep() )
{
Demo();
}


WHAT’S NEXT?

•When a movie is added
•Show notiﬁcation
•Show posters
•Show reviews

SUMMARY


TO FINALIZE

• Why EA reduces • How would it work with
complexity? web applications?

• What’s the difference with • What
about
Event Sourcing? WeakReferences?

• So, wouldthat mean we are • What about polymorphic
doing CQRS? event handling?


RESOURCES

• Email: amir@barylko.com

• Twitter: @abarylko

• Slides and code: http://bit.ly/orthoslides


RESOURCES II

•Coupling: http://bit.ly/yo5AK7

•Event Aggregator: http://bit.ly/zL1LrG
•MavenThought Commons: http://bit.ly/mt_commons
• Bootstrapper:http://bit.ly/xHNiKB
• Windsor Container:http://bit.ly/AmodqG
• Castle Dynamic Proxy: http://bit.ly/wihﬁd


SOFTWARE QUALITY
WORKSHOP
• When: May 4, 10-11, 16-17

• More info: http://www.maventhought.com


PRDCW-avent-aggregator

Recomendados

Recomendados

Mais conteúdo relacionado

Semelhante a PRDCW-avent-aggregator

Semelhante a PRDCW-avent-aggregator (20)

Mais de Amir Barylko

Mais de Amir Barylko (20)

Último

Último (20)

PRDCW-avent-aggregator