PRDCW-avent-aggregator

AMIR BARYLKO

DECOUPLINGWITH THE

EVENT AGGREGATOR

Amir Barylko - Event Aggregator MavenThought Inc.

WHO AM I?

•Quality Expert

• Architect

•Developer

•Mentor

• Great cook

• The one who’s entertaining you for the next hour!


RESOURCES

• Email: [email protected]

• Twitter : @abarylko

• Blog: http://www.orthocoders.com

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


INTROCouplingCohesion

DependenciesDependency 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 ABOUTDEPENDENCIES


HARDCODEDDEPENDENCIES

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>());


REFACTORINGWhat’s wrong?

Event AggregatorDemo

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


Library

WHAT I’D LIKE

Reviews

Posters

????


EVENT AGGREGATOR


THE PATTERN

Channel events from multiple o b j e c t s i n t o 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 complexity?

•What’s the difference with Event Sourcing?

• So, would that mean we are doing CQRS?

• How would it work with web applications?

•What about WeakReferences?

•What about polymorphic event handling?


RESOURCES

• Email: [email protected]

• 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

Technology

PRDCW-avent-aggregator