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Component-Driven Web Development in Ruby
Brian Sam-Bodden
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Components on the Web
Events and Event Handlers➡Communication between components is in the form of events
➡Components interested in an event provide a handler
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Transparent State Management➡Minimize explicit interaction with the HTTP session
➡Components are full-blow objects with rich behavior and state
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Reusable Components➡More that just reusable output generators, true OO constructs
➡Reuse views and logic in a convenient bundle
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➡Composable: Components made of Components
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What is Trellis?
Components➡Easy to build, easy to reuse
➡Encapsulate complexity in components, keep application simple
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➡MVC all the way!
Magic Like Rails!➡A DSL for Component-Oriented Ruby Web Development
➡Some new concepts and many old ones (done the Ruby way!)
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A Micro-Framework➡Small like Camping and Sinatra
➡Designed for Small Apps, Many Mounts, Complex Pages
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What is Trellis?✓declares pages used
✓declares a home page
✓dispatches request to pages
✓defines a template
✓handles events
✓dispatches events to components
✓means of communication
✓point to point
✓publish / subscribe
✓provides reusable logic
✓responds to events
✓stateless or stateful
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A lot of ideas (stolen) from...
✓Tapestry
✓Rails✓Camping
✓Sinatra
✓Seaside✓WebObjects
✓Iowa
✓Wee
What is Trellis?
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Built on Rack!
What is Trellis?
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Hello World
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✓1 Ruby File
✓1 XHTML Template
Hello World
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✓1 Ruby File
✓Inline Template using Markaby
All Ruby - Single File
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✓ 1 Application class with an entry point (a “home” page)
✓ 1 Page class with an instance variable @current_time
✓ 1 Page template embedded in the
page class
✓Template using 2 Trellis components:
Value and PageLink
✓ Template has access to page instance variables
✓ PageLink creates a hyperlink to an application Page
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It’s a Ruby program, just run it!
Application#start() launches the Trellis application w/ Mongrel on port 3000
Launching
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Application Navigation
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In Trellis page navigation is controlled by the return value of
an event handler method
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The Hi-Lo Web Application is the simple number guessing game
Start Guess GameOver
Pick a number
Number correctly guessedAn opening/welcoming page
HILO
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The Hi-Lo Web Application structure consists of 1 Ruby file and
3 XHTML templates
HILO
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The HiLoGame Trellis Application class defines the home page and any
other available pages
HILO
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✓It provides an event handler called on_select() that sets the target value on the guess page
✓The Start declares the pages it can navigate to (:guess is the symbol for the Guess page)
✓ Injected pages get their own instance variable (:guess -‐> @guess -‐> Guess)
✓If the return value of the method is a Page instance then navigate to that page
HILO
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Ok, so far so good. But, where does the on_select event come from?
HILO
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✓The ActionLink generates URLs in the form
Trellis’ default routing scheme is:
HILO
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✓ It provides an event handler called on_select_from_link(value)
✓The Guess page can only navigate to the GameOver page , see pages :game_over
✓ on_select_from_link implements a simple state machine navigation. If the guessed value:
➡ ...matches the target value then navigate to the GameOver page
➡ ...does not match the target value then navigate to the Guess page
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✓The Guess page uses several components to generate the HTML:
➡Value (<trellis:value>): outputs the value of the Page instance variable @message
➡Loop (<trellis:loop>) that repeats from 1..10 and makes the local variable guess available inside the loop
➡ Value (<trellis:value>) outputs the value of the guess local variable as the contents of the ActionLink
➡ActionLink (<trellis:action_link>): “link” which creates a hyperlink passing the guess as a parameter
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The guess’ page two states
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✓The GameOver page uses the value of @count in the message
✓The GameOver outputs a message with how many tries it took to guess the number
➡ PageLink (<trellis:page_link>): which creates a hyperlink to navigate back to the Start page
✓The GameOver page uses 1 component:
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Hangman
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Hangman is similar to Hi-Lo but it uses a few more features of Trellis
Hangman
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Static resources can be mounted using the map_static method
Hangman
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Hangman
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Templates
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Designer friendly HTML Templates
The Remove (<trellis:remove>) component allows for preview elements
HTML Templates
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Inline or external (.haml) templates:
HAML
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The Skinny on Components
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The Loop component is a typical stateless component, a.k.a a simple tag
The Loop component is a Trellis core component
A Stateless Component
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Components become full blown OO citizens when they combine state and logic in a
reusable package
A Stateful Component
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The Counter components keeps a countpage
on_add
@counter_1
reset
on_subtract
view<trellis:counter tid="one" />
<trellis:action_link tid="reset">
reset
@counter_2
reset
@counter_3
on_add source=counter_1
reset
A Stateful Component
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A Stateful Counter
Component
A Stateful Component
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{{
Reuse: The defining characteristic of a Component
A Stateful Component
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Yes, I stole this demo from Seaside!
A Stateful Component
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Encapsulate Complexity
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A Model Grid Component
Encapsulate Complexity
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Routing
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Trellis supports routing at the page level
Clean Routes
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Routes are sorted according to their “matchability”
Route Sorting
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Filters
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Trellis supports “before”, “around” and “after” filters
✓ Filters are defined at the Application level
✓ and applied at the Page level
Filters
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Testing
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Trellis can use Rack::Test w/ RSpecTesting
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Open Questions & What’s Next
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✓Testing: Rack provides Rack::MockRequest
✓Sessions: Anything that Rack can support
✓CRUD: Either dynamically generated Pages (like old Rails scaffold) or a code generator. But always using
components!
✓AJAX: Planning a JQuery-based set of components
Open Questions
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✓ Deployment: Hey is Rack!
✓Persistence: You pick. I’m developing data-aware components with a pluggable ORM
✓Is it ready?: Trellis is an infant (on version 0.1.1)
Open Questions
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Rack: http://rack.rubyforge.orgRadius: http://radius.rubyforge.orgNokogiri: http://nokogiri.orgREXML: http://www.germane-software.com/software/rexml
Builder: http://builder.rubyforge.orgPaginator: http://paginator.rubyforge.orgTrellis
Trellis @ GitHub: http://github.com/bsbodden/trellis
Trellis @ RubyForge: http://rubyforge.org/projects/trellisTrellis Website: http://www.trellisframework.org
Resources
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http://www.trellisframework.orgBlog
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Come to the South West
Proof of Residence Not Required :-)57
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