Taming Dependency Chaos with Inversion of Control Containers

St Louis Day of .NET 2011

Taming Dependency Chaoswith Inversion of Control Containers

Steve BohlenSenior Software EngineerSpringSource/VMware

E-Mail: [email protected]: http://blog.unhandled-exceptions.comTwitter: @sbohlen


Do I suck?Let me (and the world) know!

http://spkr8.com/t/8097


Who am I?• …and why should you care?• Steve Bohlen• I Read Books + Write Software• vs. “Read Software + Write Books”

• Blog, Screencast, Speak, Share, Learn


Steve BohlenNearly 20 years developing softwareLISP, Delphi, C/C++, VB, VB.NET, C#Senior Engineer Springsource/VMwareCo-Founder, NYC Alt.Net User Group

http://nyalt.netCo-Organizer, NYC DDD User Group

http://dddnyc.orgContributor: various OSS projects

Nhibernate http://www.nhforge.orgNDbUnit http://www.googlecode.com/ndbunitSpring.NET http://www.springframework.net

blog: http://blog.unhandled-exceptions.come-mail: [email protected]: @sbohlen

CYND D D


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How much can you keep in your Head?


Our Application (or class, or method, etc.)


First Attempt at Decomposition

Components!


Ideal Decomposition Level

Units!


The Challenge:Turning this into something useful

Decomposition carries overhead…

…of re-composition for meaningful work!


…easily!

The Goal:Units Assembled into Something Useful…


Code Demo: Refactoring for Decomposition


Reviewing Our Dependency Graph after Decomposition

Logger

ConnectionManager

DataSorter

Logger

Logger

Logger

DataAccessWorker

DataPrinter Logger


Code Demo: Refactoring to Ease (Re-)Composition


Reviewing Our Dependency Graph after IoC

ConnectionManager

DataSorter

Logger

DataAccess

Worker

Container

Construction Dependency

Graph

Functional Dependencies

Remain as BeforeDataPrinter


Aspect-Oriented Programming (AOP)


(one of) The Challenges ofOO Software Design

• Not all common behaviors can be efficiently modeled by OO paradigms– Inheritance, Dependency Injection / Inversion of Control

• Simple Examples– Logging, Authorization, Transactions, Exceptions

• …more…

• We call these concerns of our application– They are all things our objects must ‘concern’ themselves with doing

• Because they cut across many objects in our application…– …we call them cross-cutting concerns


Example: Logging by Inheritance

public abstract class LoggingBase{ protected void Log(string msg) {…}} Public class Service1 : LoggingBase {…}

Public class Service2 : LoggingBase {…}

Public class Service3 : LoggingBase {…}Common Abstract

Base Class …

Awkward!

Rigid hierarchy!

How do you add logging after you design your application???

Inherit from Common

Base


Public class Service1{ public Service1 (Logger logger) { _logger = logger; }}

Example: Logging by Dependency Injection

Public class Logger{ public void Log(string msg) {…}}

Dependency

Awkward! Inject Logger

Everywhere!

How do you add logging after you design your application???

Constructor Injection


The Promise of Aspect-Oriented Programming

• All (most) applications have these cross-cutting concerns– For fun (and because it’s a common convention) let’s call

them Aspects• Aspects can be applied to objects in our solution using

AOP tools– Broadly applied to many classes in our solution– Minimally-invasive– Non-Manual introduction of Aspects

• Not by literal coding (directly)


Understanding AOP Terms

Cross-Cutting Concernsthe ‘problem’ we want to solve

Advicecode that solves the problem

Pointcutwhere to apply the Advice

AspectPointcut + Advice = Aspect


Code Demo: Defining and Applying Aspects


Reviewing Our Dependency Graph after IoC

ConnectionManager

DataSorter

Logger

DataAccess

DoSomeWork

Container

Construction Dependency

Graph

Functional Dependencies

Remain as BeforeDataPrinter


Reviewing Our Dependency Graph after AOP

ConnectionManager

DataAccess

DoSomeWork

Container

DataSorter

Logger

Logger

Logger

Logger

DataPrinter Logger


Understanding the Mechanics of AOP

Advised Type Advice

Your Code

Type with Advice Applied

IoC


Thinking About Re-Assembly

Presto!


Dependency Injection Frameworks• StructureMap• Spring.NET• Castle Windsor• NInject• Funq• Unity• More…


fini

Steve BohlenSenior Software EngineerSpringSource/VMware

E-Mail: [email protected]: http://blog.unhandled-exceptions.comTwitter: @sbohlen

http://spkr8.com/t/8097

Taming Dependency Chaos with Inversion of Control Containers

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