SOLIDify Your MicrosoftASP.NET MVC Applications

Simon LarocheArchitecte LogicielPCMS Conseilslaroche@pcms.com

Risks of Poorly Designed Code• Difficult and Expensive to Maintain• Buggy• Speed of development degrades rapidly• Longer and longer test cycles

• A BIG BALL OF MUD is a casually, even haphazardly, structured system. Its organization, if one can call it that, is dictated more by expediency than design.http://www.laputan.org/mud/ http://en.wikipedia.org/wiki/Big_ball_of_mud

What is ASP.NET MVC?• Model• The representation of the business rules and data

• View• The representation of a single UI component

(a form or page, typically)• Controller• Maintains the logic of which View to display, and what data

the view needs.

ASP.NET Runtime

MVC

Controller

View

ModelRequest

Response

2

3

14

demoA Simple ASP.NET MVC Application

Benefits of OOP• -ilities• Reliability• Extensibility• Maintainability• Flexibility

• Management of Complexity

S O L I D Principles

SOLID Development Principles• SRP – Single Responsibility Principle• OCP – Open / Closed Principle• LSP – Liskov Substitution Principle• ISP – Interface Segregation Principle• DIP – Dependency Inversion Principle

SRP: What’s a Responsibility?• Persistence• Logging• Exception Handling• Formatting• Rendering / User Interface

• “A class should have one, and only one, reason to change.”

demoSRP Violation

OCP: Changes = New Code• “Modules should be open for extension, but closed for

modification.”

• Adding features should be handled by adding new code, not changing existing code.

demoOCP Violation

LSP: Subclasses Extend, Not Remove

• “Derived classes must be usable through the base class interface without the need for the user to know the difference”

• Subclasses cannot remove functionality, or change expected behaviors, of classes from which they inherit

demoLSP Violation

ISP: Clients Control Interfaces• “Separate interfaces so callers are only dependent on

what they actually use”• Avoid “fat” interfaces• Tailor interfaces to clients• Consider packaging interface with client

demoISP Violation

DIP: Depend on Abstractions• “Inject” dependencies into classes• Infrastructure should depend on core domain classes,

not the other way around• Classes should not decide particulars of how their

collaborators’ work is done – separate concern

DIP: Depend on Abstractions

DIP: Depend on Abstractions

demoDIP Violation

Simple Design Rules• Runs all the tests• Contains no duplication• Expresses the intent of the programmer• Minimizes the number of classes and methods

• The rules are given in order of importance.

Kent Beck, Extreme Programming Explained

Don’t Repeat Yourself (DRY)• "Every piece of knowledge must have a single,

unambiguous, authoritative representation within a system."

• Eliminating duplication is at the heart of many design patterns and OOP principles

demoRefactoring : Make It Right

Recommended Books• Agile Software Development

• Agile Principles, Patterns, and Practices in C#

• Clean Code

All written by Robert C. “Uncle Bob” MartinAlso see: http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod

Q & A