Ajax Rails

Ajax on Rails
Stuart Halloway and Justin Gehtland
Copyright 2005-6 Relevance, LLC

Ajax on Rails Slide 1 of 54 www.codecite.com

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Rails's Role in Ajax


Agenda

Prototype Support
Ajax requests
auto-update
UI observers
Scriptaculous Helpers
effects
widgets
JavaScript Generation
JavaScriptGenerator
rjs
JSON

What is Prototype?

Core Support for Dynamic Web Apps
Hides Browser Oddities
Used by Scriptaculous and Rico
Driven and Inspired by Ruby on Rails
Simple and Elegant


Prototype's Role in Ajax


Example: Ajax Search

Create a No-Op Form
Prototype Helper Observes User Action
Prototype Helper Submits Ajax Request
Server Renders a Partial
Update innerHTML of a Single Page Element


Creating a No-Op Form
<%= start_form_tag('javascript:void%200',
{:method=> 'filter'}) %>


Observing a Field By DOM ID
<%= observe_field :search,
:frequency => 0.5,
:update => 'ajaxWrapper',
:complete=>quot;Element.hide('spinner')quot;,
:before=>quot;Element.show('spinner')quot;,
:with=>quot;'search=' + encodeURIComponent(value)quot;,
:url=>{:action=>'search', :only_path => false} %>


Frequency to Check for Field Changes
:frequency => 0.5,


DOM ID to Update With Results
:frequency => 0.5,


Show/Hide Progress Indicator
:frequency => 0.5,


Query Parameters
:frequency => 0.5,


Server URL
:frequency => 0.5,


Why Full Path?
:frequency => 0.5,

Pragforms Intended for Cross-Site Scripting
Most Ajax Apps Will Not Need This


Rendered HTML + JavaScript
<input id=quot;searchquot; name=quot;searchquot; type=quot;textquot; value=quot;quot; />
<script type=quot;text/javascriptquot;>
//<![CDATA[
new Form.Element.Observer('search', 0.5, function(element, value) {
Element.show('spinner');
new Ajax.Updater('ajaxWrapper',
'http://localhost:3010/user/search', {
onComplete:function(request){
Element.hide('spinner');
},
parameters:'search=' + encodeURIComponent(value)
})
})
//]]>
</script>


Server Side Renders a Partial
def search
if params[:search] && params[:search].size>0
@user_pages, @users = paginate :users,
:per_page => 10,
:order => order_from_params,
:conditions=>User.conditions_by_like(params[:search])
logger.info @users.size
else
list
end
# params[:action] lets search and sort get _search and _sort
render :partial=>params[:action], :layout=>false
end


Server Side Implementation Does Not Use Layout
def search
if params[:search] && params[:search].size>0
@user_pages, @users = paginate :users,
:per_page => 10,
:order => order_from_params,
:conditions=>User.conditions_by_like(params[:search])
logger.info @users.size
else
list
end
# params[:action] lets search and sort get _search and _sort
render :partial=>params[:action], :layout=>false
end


Generalizing From The Search Example

Rails Providers Helper Methods Like observe_field
Helpers Generate JavaScript Code
Options Passed Through to Prototype/Scriptaculous
ruby hashes become JSON notation
Helpers Share Many Common Options


XHR Helper Methods
Method Trigger
link_to_remote user clicks a link
form_remote_tag user submits a form
remote_form_for user submits a form
observe_field user changes a field
observe_form user changes any field in a form
submit_to_remote user clicks button


Degradable Ajax

Ajax Apps That Also Function as Plain Old Web Pages
'Same URL' Strategy
pass Ajax-specific header
use partial for Ajax
wrap partial in template/layout for POW
'Different URL' Strategy
Ajax requests to one URL
Non-Ajax requests to a different URL


Degrading on Same URL


Degrading to Different URL
<%= link_to_remote('link',
{:update=>'jscheck'},
:href=>url_for(:action=>'no_javascript')) %>
<%= form_remote_tag(:update=>'jscheck',
:url=>{:action=>'yes_javascript'},
:html=>{:action=>'no_javascript', :method=>'post'}) %>


What is Scriptaculous?

Effects and Widgets Library
Builds on Prototype
Driven and Inspired by Ruby on Rails
Simple and Elegant


Scriptaculous's Role in Ajax


Autocomplete

Popup List of Choices
Load Possible Matches While User Edits
Several Helper Methods
Simplest Version Assumes AR-Style Model Object


Text Input
<%= text_field 'user', 'favorite_language' %></p>
<div class=quot;auto_completequot;
id=quot;user_favorite_language_auto_completequot;></div>
<%= auto_complete_field :user_favorite_language,
:url=>{:action=>'autocomplete_favorite_language'} %>


DOM ID To AutoComplete


Placeholder DIV For Suggestions


Ajax Options (URL Required)


Server Returns Simple HTML List
<ul class=quot;autocomplete_listquot;>
<% @languages.each do |l| %>
<li class=quot;autocomplete_itemquot;><%= l %></li>
<% end %>
</ul>


Drag and Drop

Mark Elements as Draggable
Mark Elements as Drop Targets
Specify Callbacks


Naming Convention: Model_Id
<ul id='pending_todo_list'>
<% @pending_todos.each do |item| %>
<% domid = quot;todo_#{item.id}quot; %>
<li class=quot;pending_todoquot; id='<%= domid %>'><%= item.name %></li>
<%= draggable_element(domid, :ghosting=>true, :revert=>true) %>
<% end %>
</ul>


Show Ghost Image While Dragging
<% end %>
</ul>


Snap Image Back After Drag
<% end %>
</ul>


DOM ID of Drop Target
<%= drop_receiving_element('pending_todos', :accept=>'completed_todo',
:complete=>quot;$('spinner').hide();quot;,
:before=>quot;$('spinner').show();quot;,
:hoverclass=>'hover',
:with=>quot;'todo=' + encodeURIComponent(element.id.split('_').last())quot;,
:url=>{:action=>:todo_pending, :id=>@user})%>


Only Accept Drops With Certain CSS Styles


Various Ajax Options


Set This CSS Class When a Valid Droppable Hovers


Query Follows Naming Convention


Distinct Style for Drop Areas
<style>
.hover {
background-color: #888888;
}
#pending_todos ul li, #completed_todos ul li {
list-style: none;
cursor: -moz-grab;
}
#pending_todos, #completed_todos {
border: 1px solid gray;
}


Distinct Style for Valid Drops on Hover
<style>
.hover {
background-color: #888888;
}
#pending_todos ul li, #completed_todos ul li {
list-style: none;
cursor: -moz-grab;
}
#pending_todos, #completed_todos {
border: 1px solid gray;
}


JavaScriptGenerator and RJS Templates

Added to Edge November 2005
Call Ruby Methods on Server-Side page Object
Generates JavaScript to Execute on Client
Methods for Prototype and Scriptaculous
Easy to Add Your Own


Some Basic Generator Calls
RJS Expression (Server) Generated JavaScript on Client
page.alert('someMessage') alert(quot;someMessagequot;);
page.redirect_to(:action=>'foo') window.location.href = quot;http://www.example.com/fooquot;;
page.call('myFunc', 'a_string', 42) myFunc(quot;a_stringquot;, 42);
page.assign('myVar', 42) myVar = 42;


Some Prototype Generator Calls
RJS Expression (Server) Generated JavaScript on Client
page.show('someDomId') Element.show(quot;someDomIdquot;);
page.hide('someDomId') Element.hide(quot;someDomIdquot;);
page.toggle('someDomId') Element.toggle(quot;someDomIdquot;);


Uses For JavaScriptGenerator

Update More Than One DOM Element
Update Element And Apply Behavior
Server Takes Control of The Page


Rendering JavaScript From the Controller
render :update do |page|
page.replace_html 'pending_todos', :partial => 'pending_todos'
page.replace_html 'completed_todos', :partial => 'completed_todos'
page.sortable quot;pending_todo_listquot;,
:url=>{:action=>:sort_pending_todos, :id=>@user}
end


Drag Move Updates More Than One Element
end


Drag Move Resets Sortable Behavior
end


Invoking UI Effects
def update_many(options)
options.each do |k,v|
page.replace_html k, :partial=>v
page.visual_effect :highlight, k
end
end
end


RJS Templates

View Files That End in .rjs
Same Object Model as render :update
Invoke Methods on page
Generated JavaScript Executes on Client


JSON Support

Rails Adds to_json to Objects
implemented in ActiveSupport::JSON
Used For Model-Centric Ajax


JSON Example: Periodically Updating Chat
class ChatJsonController < ApplicationController
def retrieve_chats
headers['Content-Type'] = quot;text/jsonquot;
@chats = get_chats
render :text=>@chats.to_json
end
end


References

Resources
Codecite (Presentations and Code Samples), http://www.codecite.com
Relevance Consulting and Development, http://www.relevancellc.com/main/services
Relevance Training, http://www.relevancellc.com/main/training
Relevance Weblog, http://blogs.relevancellc.com

Projects Cited
Ajax Labs, http://codecite.com/projects/ajax_labs.zip
Rails Exploration Application, http://codecite.com/projects/rails_xt.zip
Pragmatic Chat Sample Application, http://codecite.com/projects/pragmatic_chat.zip


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