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Ruby-on-Rails and AJAX

Java and Flash offer real alternatives for those trying to build web applications that function more like desktop applications. However, they have their shortcomings. AJAX overcomes these shortcomings -- especially if you use Ruby on Rails.

Author Info:
By: A.P.Rajshekhar
Rating: 5 stars5 stars5 stars5 stars5 stars / 31
March 27, 2007
  1. · Ruby-on-Rails and AJAX
  2. · AJAX: an Overview
  3. · Implementing AJAX
  4. · Ruby-on-Rails and AJAX

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Ruby-on-Rails and AJAX - Ruby-on-Rails and AJAX
(Page 4 of 4 )

In real world applications one of the most required functionalities is to populate a combo box based on the data entered in a preceding field such as a text box or another combo box. In this example, I will be developing such a part for an application. This can be used with any application with slight modifications. It contains two components:

index.rhtml - the view which contains the combo box to be filled and the
                     combo box on the basis of which the filling has to be done

PopulateController - the controller containing the action required for the
                                 populating of the combo box.

Here is the index.rhtml:

<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<%= javascript_include_tag "prototype" %>
<title>Ajax Rails &amp; Select lists</title>
<%= form_remote_tag(:update => "sel_con",:url => {
      :action => :create_select },
      :position => "top",:success => "$('sel_con').innerHTML=''" ) %>
Please select a sports category:
<%= select_tag "categories",
"<option>Team</option><option>Individual</option>" %>
<div id="sel_con"></div>
<%= submit_tag "Show Sports" %>
<%= end_form_tag %>

The combo box contains two values, team and individual. Based on the selection the second combo has to be populated and shown at the div having the id sel_con. If team is selected by the user, the second combo box would be filled with team events whereas in the case of individual, individual event is populated. The form_remote_tag is passed four parameters: the id of element to be updated, the action to be called, the position in which to place the result and what has to be done if the request is successfully executed. In this case the inner HTML is set to no value i.e. "". Next is the controller:

class PopulateController < ApplicationController
def index

  def create_select

    indArr=["Nordic Skiing", "Inline Skating","Tennis",
      "Triathlon","Road Racing","Figure Skating",
      "Weight Lifting","Speed Skating","Snowboarding"];

    if params[:categories].index('Team') != nil
render :partial => "options",
:locals => { :sports => teamArr,:sptype => "team"}
elsif params[:categories].index('Individual') != nil
render :partial => "options",
:locals => { :sports => indArr, :sptype => "individual" }
str="<select id='individual' name='individual'>
render :text => str;

    #end method
#end class definition

The create_select is the action where the logic for creating and populating the second combo box goes. First it creates two arrays with team and individual sports events. Then based on the parameter received, the combo box is created and populated. This is done in the statement

render :partial => "options",
:locals => { :sports => teamArr,:sptype => "team"}

Now let's look at _options.rhtml which is a partial template i.e. the a piece of HTML code that can be used again and again. Here is the code:

<select id="<%= sptype %>" name="<%= sptype %>">
<% sports.each do |sport| %>
<option><%= sport %></option>
<% end %>

It first gives the combo box an id, iterates through the array passed and populates the combo box. That's it. This completes the application. Though I had mentioned four libraries, I have introduced only one of them. In the next discussion, I will be focusing on UI using the other three libraries. Till then..

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