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XML Reference Guide

📄 Contents

  1. XML Reference Guide
  2. Overview
  3. What Is XML?
  4. Informit Articles and Sample Chapters
  5. Books and e-Books
  6. Official Documentation
  7. Table of Contents
  8. The Document Object Model
  9. Informit Articles and Sample Chapters
  10. Books and e-Books
  11. Official Documentation
  12. DOM and Java
  13. Informit Articles and Sample Chapters
  14. Books and e-Books
  15. Implementations
  16. DOM and JavaScript
  17. Using a Repeater
  18. Repeaters and XML
  19. Repeater Resources
  20. DOM and .NET
  21. Informit Articles and Sample Chapters
  22. Books and e-Books
  23. Documentation and Downloads
  24. DOM and C++
  25. DOM and C++ Resources
  26. DOM and Perl
  27. DOM and Perl Resources
  28. DOM and PHP
  29. DOM and PHP Resources
  30. DOM Level 3
  31. DOM Level 3 Core
  32. DOM Level 3 Load and Save
  33. DOM Level 3 XPath
  34. DOM Level 3 Validation
  35. Informit Articles and Sample Chapters
  36. Books and e-Books
  37. Documentation and Implementations
  38. The Simple API for XML (SAX)
  39. Informit Articles and Sample Chapters
  40. Books and e-Books
  41. Official Documentation
  42. SAX and Java
  43. Informit Articles and Sample Chapters
  44. Books and e-Books
  45. SAX and .NET
  46. Informit Articles and Sample Chapters
  47. SAX and Perl
  48. SAX and Perl Resources
  49. SAX and PHP
  50. SAX and PHP Resources
  51. Validation
  52. Informit Articles and Sample Chapters
  53. Books and e-Books
  54. Official Documentation
  55. Document Type Definitions (DTDs)
  56. Informit Articles and Sample Chapters
  57. Books and e-Books
  58. Official Documentation
  59. XML Schemas
  60. Informit Articles and Sample Chapters
  61. Books and e-Books
  62. Official Documentation
  63. RELAX NG
  64. Informit Articles and Sample Chapters
  65. Books and e-Books
  66. Official Documentation
  67. Schematron
  68. Official Documentation and Implementations
  69. Validation in Applications
  70. Informit Articles and Sample Chapters
  71. Books and e-Books
  72. XSL Transformations (XSLT)
  73. Informit Articles and Sample Chapters
  74. Books and e-Books
  75. Official Documentation
  76. XSLT in Java
  77. Java in XSLT Resources
  78. XSLT and RSS in .NET
  79. XSLT and RSS in .NET Resources
  80. XSL-FO
  81. Informit Articles and Sample Chapters
  82. Books and e-Books
  83. Official Documentation
  84. XPath
  85. Informit Articles and Sample Chapters
  86. Books and e-Books
  87. Official Documentation
  88. XML Base
  89. Informit Articles and Sample Chapters
  90. Official Documentation
  91. XHTML
  92. Informit Articles and Sample Chapters
  93. Books and e-Books
  94. Official Documentation
  95. XHTML 2.0
  96. Documentation
  97. Cascading Style Sheets
  98. Informit Articles and Sample Chapters
  99. Books and e-Books
  100. Official Documentation
  101. XUL
  102. XUL References
  103. XML Events
  104. XML Events Resources
  105. XML Data Binding
  106. Informit Articles and Sample Chapters
  107. Books and e-Books
  108. Specifications
  109. Implementations
  110. XML and Databases
  111. Informit Articles and Sample Chapters
  112. Books and e-Books
  113. Online Resources
  114. Official Documentation
  115. SQL Server and FOR XML
  116. Informit Articles and Sample Chapters
  117. Books and e-Books
  118. Documentation and Implementations
  119. Service Oriented Architecture
  120. Web Services
  121. Informit Articles and Sample Chapters
  122. Books and e-Books
  123. Official Documentation
  124. Creating a Perl Web Service Client
  125. SOAP::Lite
  126. Amazon Web Services
  127. Creating the Movable Type Plug-in
  128. Perl, Amazon, and Movable Type Resources
  129. Apache Axis2
  130. REST
  131. REST Resources
  132. SOAP
  133. Informit Articles and Sample Chapters
  134. Books and e-Books
  135. Official Documentation
  136. SOAP and Java
  137. Informit Articles and Sample Chapters
  138. Books and e-Books
  139. Official Documentation
  140. WSDL
  141. Informit Articles and Sample Chapters
  142. Books and e-Books
  143. Official Documentation
  144. UDDI
  145. UDDI Resources
  146. XML-RPC
  147. XML-RPC in PHP
  148. Informit Articles and Sample Chapters
  149. Books and e-Books
  150. Official Documentation
  151. Ajax
  152. Asynchronous Javascript
  153. Client-side XSLT
  154. SAJAX and PHP
  155. Ajax Resources
  156. JSON
  157. Ruby on Rails
  158. Creating Objects
  159. Ruby Basics: Arrays and Other Sundry Bits
  160. Ruby Basics: Iterators and Persistence
  161. Starting on the Rails
  162. Rails and Databases
  163. Rails: Ajax and Partials
  164. Rails Resources
  165. Web Services Security
  166. Web Services Security Resources
  167. SAML
  168. Informit Articles and Sample Chapters
  169. Books and e-Books
  170. Specification and Implementation
  171. XML Digital Signatures
  172. XML Digital Signatures Resources
  173. XML Key Management Services
  174. Resources for XML Key Management Services
  175. Internationalization
  176. Resources
  177. Grid Computing
  178. Grid Resources
  179. Web Services Resource Framework
  180. Web Services Resource Framework Resources
  181. WS-Addressing
  182. WS-Addressing Resources
  183. WS-Notifications
  184. New Languages: XML in Use
  185. Informit Articles and Sample Chapters
  186. Books and e-Books
  187. Official Documentation
  188. Google Web Toolkit
  189. GWT Basic Interactivity
  190. Google Sitemaps
  191. Google Sitemaps Resources
  192. Accessibility
  193. Web Accessibility
  194. XML Accessibility
  195. Accessibility Resources
  196. The Semantic Web
  197. Defining a New Ontology
  198. OWL: Web Ontology Language
  199. Semantic Web Resources
  200. Google Base
  201. Microformats
  202. StructuredBlogging
  203. Live Clipboard
  204. WML
  205. XHTML-MP
  206. WML Resources
  207. Google Web Services
  208. Google Web Services API
  209. Google Web Services Resources
  210. The Yahoo! Web Services Interface
  211. Yahoo! Web Services and PHP
  212. Yahoo! Web Services Resources
  213. eBay REST API
  214. WordML
  215. WordML Part 2: Lists
  216. WordML Part 3: Tables
  217. WordML Resources
  218. DocBook
  219. Articles
  220. Books and e-Books
  221. Official Documentation and Implementations
  222. XML Query
  223. Informit Articles and Sample Chapters
  224. Books and e-Books
  225. Official Documentation
  226. XForms
  227. Informit Articles and Sample Chapters
  228. Books and e-Books
  229. Official Documentation
  230. Resource Description Framework (RDF)
  231. Informit Articles and Sample Chapters
  232. Books and e-Books
  233. Official Documentation
  234. Topic Maps
  235. Informit Articles and Sample Chapters
  236. Books and e-Books
  237. Official Documentation, Implementations, and Other Resources
  238. Rich Site Summary (RSS)
  239. Informit Articles and Sample Chapters
  240. Books and e-Books
  241. Official Documentation
  242. Simple Sharing Extensions (SSE)
  243. Atom
  244. Podcasting
  245. Podcasting Resources
  246. Scalable Vector Graphics (SVG)
  247. Informit Articles and Sample Chapters
  248. Books and e-Books
  249. Official Documentation
  250. OPML
  251. OPML Resources
  252. Summary
  253. Projects
  254. JavaScript TimeTracker: JSON and PHP
  255. The Javascript Timetracker
  256. Refactoring to Javascript Objects
  257. Creating the Yahoo! Widget
  258. Web Mashup
  259. Google Maps
  260. Indeed Mashup
  261. Mashup Part 3: Putting It All Together
  262. Additional Resources
  263. Frequently Asked Questions About XML
  264. What's XML, and why should I use it?
  265. What's a well-formed document?
  266. What's the difference between XML and HTML?
  267. What's the difference between HTML and XHTML?
  268. Can I use XML in a browser?
  269. Should I use elements or attributes for my document?
  270. What's a namespace?
  271. Where can I get an XML parser?
  272. What's the difference between a well-formed document and a valid document?
  273. What's a validating parser?
  274. Should I use DOM or SAX for my application?
  275. How can I stop a SAX parser before it has parsed the entire document?
  276. 2005 Predictions
  277. 2006 Predictions
  278. Nick's Book Picks

At this point we've got the very basics of a working Rails application, and using the scaffolding we can make changes to the database. Now we're going to look at taking control of that process. We'll start by editing an existing question, and then we'll move on to adding and deleting questions.

When we last left our application, the "edit" action was being handled by the scaffolding. To change that, start by creating a template that references the specific question we want to edit:

<html>
<head>
   <title>Questions, questions questions</title>
</head>

<body>
   <h2>Edit a question</h2>

   The existing question is "<%= @thisQuestion.questionText %>"

</body>
</html>

As before, if we access this page, we have a problem:

IMAGE MISSING

The problem lies in the fact that we haven't provided a specific object from which we want the questionText attribute. To solve the problem, create the edit action in the Questions controller, question_controller.rb:

class QuestionController < ApplicationController

   model :question
   
   scaffold :question

   def index
   end

   def list
      @questions = Question.find_all
   end

   def edit
      @thisQuestion = Question.find(@params["id"])
   end

end

As you may remember, the URL includes the id of the question we're working with. As such, we can extract it from the params array. (We'll look at this array in detail in the moment, but for now just take it on faith that the id value is in it.) The find method expects to receive the ID of the object you're looking for in any model, whether it's the Question, Survey, or Answer. It's just the way that Rails has been designed; models automatically have the find method, which takes the id of the particular object, goes to the database, and populates an object with the data it finds for that row.

(To digress for a moment, you can also find a group of objects, which are passed as an array, using the find_all method. With no arguments, this method finds all records. You also have the option of providing a filter, such as "id > 25" or "status = 'finished'" to limit the records you get back.)

Once we find it, we assign it to the thisQuestion variable, which gets passed to the template:

IMAGE MISSING

So now we have the correct question, so let's build an editing form around it in the "edit" template:

<html>
<head>
   <title>Questions, questions questions</title>
</head>
<body>

   <h2>Edit a question</h2>

  <form method="post" 
       action="/question/editExistingQuestion/<%= @thisQuestion.id %>">
    Edit the question: <br />   
                                             
    <%= text_field("theExistingQuestion", "questionText", 
                      "value" => @thisQuestion.questionText) %>                
    <br />

    <input type="submit" value="Save Question">
  </form>

</body>
</html>

OK, let's start at the top, with the form element. If you're familiar with HTML, you know that the action attribute represents the URL to which the data will be sent. In Rails, this means we want the URL that looks something like this:

http://localhost:3000/question/editExistingQuestion/12

In this case, the we're dealing with a question object, for which we want to perform the editExistingQuestion action, on the object with an id of 12. To replicate that in the action attribute, we construct the tag dynamically, asking Rails to add the id for the current object.

Next we have the text_field method, which takes the following arguments. First, the name of an array to which the data will belong. This will make more sense in a moment, when we see the actual data. Second, we have the name of the actual piece of data. This name should match the attribute name for the object, so Rails knows what to do with it. Finally, we have an optional HTML option that allows us to add an arbitrary attribute and value. When you have Rails render the page, either by entering the URL manually, or clicking on a "Change" link, it creates the actual form for you:

<html>
<head>
   <title>Questions, questions questions</title>
</head>

<body>
   <h2>Edit a question</h2>

  <form method="post" action="/question/editExistingQuestion/12">
    Edit the question: <br />                                                  
    <input id="theExistingQuestion_questionText" 
            name="theExistingQuestion[questionText]" size="30" type="text" 
            value="What is your name?" />                
    <br />

    <input type="submit" value="Save Question">
  </form>

</body>
</html>

Notice that Rails has taken care of housekeeping issues such as creating the actual input element and adding the appropriate attributes. Notice also that the name element hints that we are actually dealing with an array. The page itself looks perfectly normal:

IMAGE MISSING

Okay, so let's see what happens if we submit the form. First we need to create an action in the controller:

...
   def edit
      @thisQuestion = Question.find(@params["id"])
   end

   def editExistingQuestion
      render_text @params.inspect
   end

end

In this case, we are simply telling Rails to print out a representation of the parameters that are being submitted with the request so that we can see them. If we then go ahead and submit the form, we should see something like this:

{"action"=>"editExistingQuestion", 
"theExistingQuestion"=>{"id"=>"12", "questionText"=>"What is your name?"}, 
"controller"=>"question"}

Notice that the parameters are actually an array that has as one of its members (specifically, the theExistingQuestion member) another array. Now let's do something with that data:

...
   def editExistingQuestion
      thisQuestion = Question.find(@params["id"])
      thisQuestion.attributes = @params["theExistingQuestion"]
      if thisQuestion.save
         render_text "Question saved.  Thank you."
      else
         render_text "Sorry, no can do."
      end
   end

end

First, as before, we're finding the specific object we want to work with. Once we have it, we can specifically assign the theExistingQuesiton array to the attributes array for the object, and everything will fall into place. That's why we made sure that the name of the field matched the name of the attribute we wanted to set.

Once we've populated the data, all we have to do to save it to the database. We can do that with the save method, which returns true if the operation is successful. Try it by making a change and submitting the form:

IMAGE MISSING

To see if it worked, click the "back" button twice, and then reload the page if necessary:

IMAGE MISSING

Well, it worked, but it wasn't very convenient. Fortunately, we can tell Rails to send us back to the list of questions automatically:

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

end

You can redirect to any action, such as "new", or even a custom action that you've created.

Adding a new record is just as easy. Start by adding a form to the list template:

<html>
<head>
   <title>Questions, questions questions</title>
</head>

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

   <% @questions.each do |@thisQuestion| %>
       <%= @thisQuestion.questionText %> 
       ( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
       <br />

   <% end %>

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

</body>
</html>

The principle is the same as editing the record, but because we don't have a specific object to deal with, we can be a bit more general in our action. We'll create the new action in a moment. The form, meanwhile, is just a typical form:

IMAGE MISSING

Now we just need to save the question when its submitted. Create the new addNewQuestion action:

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

   def addNewQuestion
      thisQuestion = Question.new
      thisQuestion.attributes = @params["newQuestion"]
      if thisQuestion.save
         redirect_to(:action => "list")
      else
         render_text "Sorry, no can do."
      end
   end

end

The process is virtually identical to editing an existing object, except that instead of populating it by finding a record in the database, we're using the Question class to create a new object. We can then populate it and save it, moving back to the list of existing questions if all goes well.

IMAGE MISSING

So what about deleting existing records? It's also a fairly simple process. Start by creating a "delete" link on the list template:

<html>
<head>
   <title>Questions, questions questions</title>
</head>

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

   <% @questions.each do |@thisQuestion| %>
       <%= @thisQuestion.questionText %> 
       ( <%= link_to("Change", :action => "edit", :id => @thisQuestion.id) %> )
       ( <%= link_to("Delete", :action => "destroy", :id => @thisQuestion.id)%> )

       <br />
   <% end %>

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

  </form> 

</body>
</html>

The only difference between this link and the previous one is the action to which it takes you. In Rails, to delete an object, you "destroy" it, so we'll keep with that as the action name.

Actually deleting it is a straightforward process:

...
      if thisQuestion.save
         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

As in the case of editing the object, we first find the appropriate one in the database, but from there we use the destroy method instead of save.

So that takes care of creating, retrieving, editing, and deleting objects from the database, which is, let's face it, most of what you do in a dynamic web application. With a little tweaking for your own purposes, you should be ready to go.

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Last Update: November 17, 2020