XML Reference Guide

Mar 14, 2003

␡

⎙ Print

< Back Page 163 of 278 Next >

We've done all the hard work, such as accessing the database, so now we can start adding bells and whistles.

The most obvious of those bells is the web-technique-du-jour, Ajax, which enables you to replace only part of a web page with new information from the server. If you have read previous sections on Ajax in general and Ajax and PHP, and you know that Ajax can be a significant challenge to pull off.

Fortunately, Ajax is just one more thing Rails makes almost childishly easy.

In this section, we'll Ajax-enable the SurveySays utility for entering Questions into the system, providing the ability to add and delete questions without reloading the "list" page. We'll also look at "partials", which enable you to easily reuse code and display logic.

As you recall, we currently have a template, or view, for the list action. (If you don't recall, go back and read previous sections.) This view lists the existing questions, along with links that enable the user to edit or delete them. It also includes a form for entering new questions.

To start adding Ajax capabilities, we'll change the "delete" links slightly by making changes to the app/views/question/list.rhtml file:

<html>

<head>
   <title>Questions, questions questions</title>
   <%= javascript_include_tag "prototype" %>
</head>

<body>
   <h2>Existing questions</h2>

   <div id="listOfQuestions">
   <% @questions.each do |@thisQuestion| %>
       <%= @thisQuestion.questionText %> 
       ( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
       ( <%= link_to_remote("Delete", :update => "listOfQuestions", 
              :url => {:action => "destroy", :id => @thisQuestion.id}) %> )

       <br />

   <% end %>
   </div>

   <br />
   <form method="post" action="addNewQuestion">
      Add a new question:                                                   
      <%= text_field("newQuestion", "questionText") %>                
      <input type="submit" value="Save Question">

   </form> 

</body>
</html>

Starting at the top, remember that Ajax is handled using JavaScript, so we first have to import the appropriate JavaScript code. The "prototype" library ships with Rails, so all you have to do is include it. Next, our goal is to change part of the page, so we'll define what part of the page were changing by creating a div called listOfQuestions. Finally, we use link_to_remote instead of link_to to tell Rails to add the Ajax code to the link.

The parameters we are using are as follows. First, we list the text for the link. Next the :update parameter lists the div to change. Finally, the :url is the code to actually call. As before, we are calling the destroy action for question @thisQuestion.id.

The page itself doesn't show any outward changes:

You can do a "view source" to see how the actual HTML changes, but the quickest way to see the changes to click the "delete" link for an existing question.

That's not quite what we wanted, of course, so let's see what happened.

We told Rails that we wanted to replace the contents of the listOfQuestions div with the output of the destroy action. To see what that is, let's look at the question_controller.rb:

...
         redirect_to(:action => "list")
      else
         render_text "Sorry, no can do."
      end
   end

   def destroy
      thisQuestion = Question.find(@params["id"])
      if thisQuestion.destroy
         redirect_to(:action => "list")
      else
         render_text "Sorry, no can do."
      end
   end

end

First we are finding and deleting the specific question, but then we defer to the list action, which outputs the entire page including the header and the form at the bottom. All of this information winds up in the listOfQuestions div, giving the illusion of a page within a page. (Actually, it's no illusion. There really is a page within the page.)

What we really need is a way to display only part of the page. In this case, it is a part of the page that displays the individual list items. In Rails, this is called a "partial". Partials are small snippets you can reuse in various places. We'll use them to display the questions.

Start by creating a new file called _questionList.rhtml. Note that the leading underscore is what designates the file as a partial, so make sure you don't forget to add it. Save the file in the app/views/question directory. Add the following code:

<%= @thisQuestion.questionText %> 
( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
( <%= link_to_remote("Delete", :update => "listOfQuestions", 
           :url => {:action => "destroy", :id => @thisQuestion.id}) %> )

<br />

Now we need to tell Rails to render the partial on the page:

...
   <h2>Existing questions</h2>

   <div id="listOfQuestions">
   <% @questions.each do |@thisQuestion| %>

       <%= render_partial "questionList", @thisQuestion %>

   <% end %>
   </div>

   <br />
   <form method="post" action="addNewQuestion">

...

First we provide the name of the partial we want to use (note that we do not reference the underscore here, just in the filename), and then the data we are passing into it. With these changes in place, you should not see any change to the actual display:

Of course you will almost always use this in the context of looping through data of some sort, so fortunately Rails provides a way to do this simply:

...
<body>
   <h2>Existing questions</h2>

   <div id="listOfQuestions">
       <%= render_collection_of_partials "questionList", @questions %>
   </div>

   <br />
   <form method="post" action="addNewQuestion">

...

The renderer_collection_of_partials function again takes the name of the partial to use, but in this case rather than a single object, it takes an array through which Rails should loop.

But we still have to tell the partial what values it's working with:

<% @thisQuestion = questionList %>

<%= @thisQuestion.questionText %> 

( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
( <%= link_to_remote("Delete", :update => "listOfQuestions", 
           :url => {:action => "destroy", :id => @thisQuestion.id}) %> )

<br />

We are simply telling Rails to associate the @thisQuestion variable with successive items in the array passed into the questionList partial.

But where does the array actually come from? It comes from the controller, which creates the array before actually executing the list view.

That works fine for the list action, but we need a way to simply display the questions all by themselves. Specifically, we need an action that does it. We'll call the action showQuestions. Start with the view, showQuestions.rhtml. It only needs one line:

<%= render_collection_of_partials "questionList", @questions %>

Now we need to create the action in the controller so that we can create the actual @questions array:

...

   def destroy
      thisQuestion = Question.find(@params["id"])
      if thisQuestion.destroy
         redirect_to(:action => "list")
      else
         render_text "Sorry, no can do."
      end
   end

   def showQuestions
       @questions = Question.find_all
   end

end

Before we move on, let's test the new action. Point your browser to:

http://localhost:3000/question/showQuestions

You should see a list of questions:

Okay now that we know that that works, and that it gives us what we need to put into the div, we need to create the action that calls showQuestions:

...
   def destroy
      thisQuestion = Question.find(@params["id"])
      if thisQuestion.destroy
         redirect_to(:action => "list")
      else
         render_text "Sorry, no can do."
      end
   end

   def deleteQuestion
      thisQuestion = Question.find(@params["id"])
      if thisQuestion.destroy
         redirect_to(:action => "showQuestions")
      else
         render_text "Sorry, no can do."
      end
   end

   def showQuestions
       @questions = Question.find_all
   end

end

Essentially this is the same as destroy, but now you can just replace the list, rather than the whole page. First add it to the _questionList.rhtml:

<% @thisQuestion = questionList %>

<%= @thisQuestion.questionText %> 

( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
( <%= link_to_remote("Delete", :update => "listOfQuestions", 
      :url => {:action => "deleteQuestion", :id => @thisQuestion.id}) %> )

<br />

Now if you open your browser to the list and click a "Delete" link, you should see just the list of questions change.

That takes care of links, but what about forms? After all, we do a lot of the same data manipulation techniques with forms as we do with links. Well, Rails provides a very similar in way of dealing with this issue for forms. Start by adjusting the list to create a new form:

...
   <div id="listOfQuestions">
       <%= render_collection_of_partials "questionList", @questions %>

   </div>

   <br />
   <%= form_remote_tag(:update => "listOfQuestions",
                       :url => { :action => :addNewQuestion } ) %>
      Add a new question:                                                   
      <%= text_field("newQuestion", "questionText") %>                
      <input type="submit" value="Save Question">

   <%= end_form_tag %>

</body>
</html>

The form here is virtually identical to its predecessor, with the exception of the Ajax enabling code, which works exactly the same way as link_to_remote. In fact, it is so similar that if you simply try it out now, you'll get the same reaction we got at the beginning of this section: a doubling of the page. What we need to do is apply the same techniques to the addNewQuestion action.

In fact, what we need is for this action to simply output the new question so that we can add it to the existing list. In the controller, alter the addNewQuestion action so that it uses the partial:

...
         render_text "Sorry, no can do."
      end
   end

   def addNewQuestion
      thisQuestion = Question.new
      thisQuestion.attributes = @params["newQuestion"]
      if thisQuestion.save
         render_text (render_partial "questionList", thisQuestion)
      else
         render_text "Sorry, no can do."
      end
   end
...

But if we submit it, we don't get quite what we want:

In a good example of the computer doing what you tell it to and not what you want it to do, Rails has told the browser to replace the entire contents of the div with the new content. But what we really want is for the new text to be added at the bottom of the list. We can do that by setting the position on the form itself:

...
...
    <br />
    <%= form_remote_tag(:update => "listOfQuestions",
                       :url => { :action => :addNewQuestion },
                       :position => "bottom") %>

       Add a new question:                                                   
       <%= text_field("newQuestion", "questionText") %>                
       <input type="submit" value="Save Question">
    <%= end_form_tag %>

</body>
</html>

Now if you try it, the new question should get added at the bottom of the div:

You can set :position values of top and bottom, which add the new content inside the div, or before and after, which add the new content outside the div.

There are plenty of other bells and whistles, but this should hold us for now.

< Back Page 163 of 278 Next >

🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Privacy Notice

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
Such marketing is consistent with applicable law and Pearson's legal obligations.
Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

As required by law.
With the consent of the individual (or their parent, if the individual is a minor)
In response to a subpoena, court order or legal process, to the extent permitted or required by law
To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
To investigate or address actual or suspected fraud or other illegal activities
To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020

Email Address