MVC Demystified: Essence of Ruby on Rails

MVC Demystified Webvisions 2007 Michael P. Jones [email_address] Understanding the Essence of Ruby on Rails

About Session
Web applications
MVC
Pix Patisserie
MVC Another Look
Rails Essence
More Rails
Rails Testing
Other MVC

About Speaker
Past
Educational and Reservation software. (Java)
Founded Code in Motion. http://codeinmotion.com/
Present
Creating custom Ruby on Rails applications.
Recovery and prevention.
Screening and Interview
PDF generation of applications
Widgets
Tailoring CMS Solutions
Radiant, Rails based CMS with extensions for business needs of the client.

Traditional Applications
Browser directly accesses page.
Does not centralize control
No content/style separation
Easy and fast to produce
Difficult to maintain

MVC Applications
Browser accesses a “controller”
Centralizes control
Clean separation of content/style
More involved to produce
Easier to maintain and expand

MVC
MVC is an Architectural Design Pattern
Separates a web application into three different modules.

Design Pattern
A pattern that has been developed to help programmers cope with common problems.
Blueprints on how to construct something.

MVC Means
Most Vexing Conundrum (Amy Hoy)
Model | View | Controller

Trip to Pix
A Patisserie in Portland
http://qwendy.typepad.com/

Typical Bakery Interaction
Request a tasty treat from the baker
http://www.pixpatisserie.com/

Baker Gathers Ingredients
Baker gathers raw ingredients to fulfill the request.
Some requests utilize same ingredients.
http://www.flickr.com/photos/moria/92792777/

Baker Select Pan
The pan dictates what the response looks like.
http://www.flickr.com/photos/tracyhunter/113563802/

Baker responds with your treat http://www.pixpatisserie.com/

Pix Flow

MVC Diagram

Controller (Baker)
Dispatches Requests and controls flow.
Centralizes access.
Interacts with Model and View.

Model (Ingredients)
Data representation and business logic.
Can be database/xml/etc
Business Logic
Examples:
User
Bike
Question

View (Pan)
Data presentation and user input.
Renders the Model in to a View.
Can be HTML/PDF/WML/Javascript
No computations, very little logic, display logic i.e. loops

MVC Diagram

MVC Advantages
Separation of interests.
Model centralizes business logic.
View centralizes display logic.
Controller centralizes application flow.
Clean separation of content/style.
Improved decoupling.
Easier testing.
Allow multiple people to work on different parts.

Rails and MVC
Rails in an MVC framework
”… Rails is such a framework that tries to remove the complexity and drudgery of MVC, while still allowing you to realize all the benefits.” - DHH (David Heinemeier Hansson)

Model: ActiveRecord
ActiveRecord is a design pattern. (Martin Fowler)
Object wraps a row in the database.
Encapsulates data access.
Contains business logic.
Handles relationships.
Handles validation.

ActiveRecord Code

View: ActionView
Renders the view.
Both .rhtml and .rxml files.
Provides master layouts.
Uses ERb (embedded ruby) for templating and control.

ActionView Code

Controller: ActionController
Controls application flow.
Controls which view to use.
Makes data available as instance variables @var
Contains several actions/defs
Controls rendering and redirection.

ActionController Code

All Together Now http://wiki.rubyonrails.org/

How it works
your_domain.com/controller/action/id
Controller has actions.
View directory has directory for each controller.
Same action name as .rhtml file
your_domain.com/bikes/edit/2
Controller: bikes
Action: edit
Id: 2

Rails Concepts
DRY (Don’t Repeat Yourself)
Convention of configuration
Generators script/generate generator_name
:symbols or ‘symbols’
represents names and strings
YAML machine parsable human readable.

More ActiveRecord
Automatically maps to a table
No XML configs
Each row is an Object
Several databases supported.
Provides
CRUD: Create, Read, Update, Destroy
Getters/Setters
Validation: validates_presence_of, validates_format_of
Callbacks: hooks into lifecycle, trigger events before/after
Finding: Person.find(:all, :conditions => [ "category IN (?)", categories], :limit => 50)

More ActiveRecord Code
Callbacks
Relations
Validation

More ActionView
Layouts
app/view/layouts/application.rhtml
Partials
_partial_view.rhtml
Reuse of common view elements
Helpers
Helper module per Controller
Contains Ruby code

More ActionView Code

More ActionController
Filters
before , after and around processing hooks
Routes
Replaces apache mod_rewrite
config/routes.rb
Caching
Has caching to improve performance
page
action
fragment

More ActionController Image

Pitfalls: Excess
Model: God Object (anti-pattern)
Too much logic in a Model, one Model too powerful.
View: Too much logic in View
Controller: Anemic Domain Model (anti-pattern)
Too much business logic in Controller.
Cargo cult programming
(over-)applying a design principle blindly without understanding the reasons. - (wikipedia)

Testing Rails
Rails has great testing framework ‘baked in’ the framework
Test stubs created when code is ‘generated’.
Unit to test models.
test/unit
Functional to test views/controllers
test/functional
Fixtures
Supply test data (yaml)

Unit Testing
Separate ‘test’ database is used.
Fixtures supply data
Variety of ‘assert’ statements.

Functional Testing
Fixture
Setup
Tests

Rake
Rake is your friend.
Database tasks
Deployment
Documentation
Testing
Cleanup

MVC Around The Web
Java
Struts, Spring
.NET
MonoRail (inspired by Rails)
Perl
Catalyst, MayPole
Php
CakePHP, Code Igniter
Python
Django, TurboGears
Ruby
Nitro, Wee

Questions?
MVC
Rails
Pix

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MVC Demystified: Essence of Ruby on Rails

by codeinmotion on May 04, 2007

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MVC Demystified: Essence of Ruby on Rails — Presentation Transcript