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

About Session <ul><li>Web applications </li></ul><ul><li>MVC
</li></ul><ul><li>Pix Patisserie </li></ul><ul><li>MVC Another Look </li></ul><ul><li>Rails Essence </li></ul><ul><li>More Rails </li></ul><ul><li>Rails Testing </li></ul><ul><li>Other MVC </li></ul>

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

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

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

MVC <ul><li>MVC is an Architectural
Design Pattern </li></ul><ul><li>Separates a web application into three different modules. </li></ul>

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

MVC Means <ul><li>Most Vexing Conundrum
(Amy Hoy) </li></ul><ul><li>Model | View | Controller </li></ul>

Trip to Pix <ul><li>A Patisserie
in Portland </li></ul>http://qwendy.typepad.com/

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

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

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

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

Pix Flow

MVC Diagram

Controller (Baker) <ul><li>Dispatches Requests and
controls flow. </li></ul><ul><li>Centralizes access. </li></ul><ul><li>Interacts with Model and View. </li></ul>

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

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

MVC Diagram

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

Rails and MVC <ul><li>Rails in
an MVC framework </li></ul><ul><li>”… 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) </li></ul>

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

ActiveRecord Code

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

ActionView Code

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

ActionController Code

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

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

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

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

More ActiveRecord Code <ul><li>Callbacks </li></ul><ul><li>Relations
</li></ul><ul><li>Validation </li></ul>

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

More ActionView Code

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

More ActionController Image

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

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

Unit Testing <ul><li>Separate ‘test’ database
is used. </li></ul><ul><li>Fixtures supply data </li></ul><ul><li>Variety of ‘assert’ statements. </li></ul>

Functional Testing <ul><li>Fixture </li></ul><ul><li>Setup </li></ul><ul><li>Tests
</li></ul>

Rake <ul><li>Rake is your friend.
</li></ul><ul><ul><li>Database tasks </li></ul></ul><ul><ul><li>Deployment </li></ul></ul><ul><ul><li>Documentation </li></ul></ul><ul><ul><li>Testing </li></ul></ul><ul><ul><li>Cleanup </li></ul></ul>

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

Questions? <ul><li>MVC </li></ul><ul><li>Rails </li></ul><ul><li>Pix </li></ul>