To Lecture Notes

IT 231 -- 10/16/12

Midterm Exam

• Go over the midterm exam.

Sending Data from a View Back to the Controller

• Recall the two PHP examples, Examples 11 and 12: GetSubmit Example and PostSubmit Example.
   
• To send data from a view to the controller, data is entered onto a form via HTML controls:
   
  
  Textfield:  
  

  <input type="text" name="txtName" size="20" />
  

  Dropdown Menu:   Discover Master Card Visa
  

  <select name="ddmCardType">
      <option value="1">Discover</option>
      <option value="2">Master Card</option>
      <option value="3">Visa</option>
  </select>
  

  Check Box:   Fulltime Student
  

  <input type="checkbox" name="txtFulltimeStatus" /> 
  Fulltime Student
  

  Radio Button:   Discover
  Master Card
  Visa
  

  <input type="radio" name="cardType" /> Discover  
  <input type="radio" name="cardType" /> Master Card  
  <input type="radio" name="cardType" 
      checked="checked" /> Visa
  

• To send data back to the server, these controls must be placed onto a form:
  

  <form name="frmMain" action="summary.php" method="get">
      ... Controls go here.
  </form>
  

• See Examples 11 and 12 that show how to submit data back to the server running PHP using HTML.
   
• In Rails, we use FormTagHelper methods (for example form_tag, text_field_tag, and submit_tag) to generate the form and the controls.
   
• We will use FormTagHelper methods for Project 5.
   
1. Form
   

   <%= form_tag 'show' do %>
   ... Controls go here.
   <% end %>
   

   1. 'show' is the action, which is taken when the submit button is clicked.
       
   2. do means that everything until the end statement is included in the form.
       
   3. The equals sign is not used in the Rails delimiter for the end statement because end is a control statement.
   
   
2. Textfield
   

   <%= text_field_tag :cel, @c, :class => 'ctrl' %>
   

   1. :cel is the name of the textfield control.
       
   2. @c is the initial value of the textfield.
   
   
3. Submit
   

   <%= submit_tag 'Convert Temperature', 
       :class => 'ctrl' %>
   

   1. 'Convert Temperature' is the text of the submit control.
       
   2. When the submit control is clicked, the action specified in the form_tag control is executed.
   
   
4. Dropdown Menu
   

   <%= select_tag :source_rate,
          options_for_select([["Dollars", "1.00000"],
                              ["Euro", "1.36749"],
                              ["Pesos", "12.6149"],
                              ["Pounds", "1.58228"]]),
          :class => 'ctrl' %>
   

   :source_rate is the name
   the option tags are the HTML option tags.
   
   
5. Radio Button
   

   <%= radio_button_tag :group, :value, true %>
   

   :group sets the button group (in a group of radio buttons, only can be checked at a time)
   :value is the value returned to the controller in a params statement
   true means that the radio button should be initially checked.
   
   
6. Check Box
   

   <%= check_box_tag :sugar, 1, false %>
   

   :sugar is the name
   1 is the value returned to the controller in a params statement
   false means that the checkbox is initially not checked.
   
   
• See Example 23 (CToF2 Example).
   
• For Project 5, we will use a different style of helper methods called FormHelper methods that interface directly with the model.
   

Catching Data Sent from a View by the Controller

• Data that are sent back to the controller from a view are caught in a params statement.
   
• For example, Example 23 contains the following ERB code:
  

  <%= form_tag 'show' do %>             
  <%= text_field_tag :cel, @cel %>
  <%= submit_tag 'Convert Temperature' %>
  <% end %>
  

• The form tag shows that the show action is taken (goes to the show view), when the submit tag is clicked.
   
• This implies that the contents of each control on the form (between form_tag and end) is sent back to the controller.
   
• The piece of data sent back to the controller is identified by the label of the corresponding controller (in this case :cel).
   
• For example, the contents of the text field is identified by the symbol :cel.
   
• The leading colon shows that :cel is a symbol, not a variable or string.
   
• Symbols are used for control names in Rails because they are processed more efficiently than strings or variables.
   
• Here is the Example 23 controller code that catches the data from the text field (identified with the symbol :celsius) in a params statement and assigns it to the variable input:
  

  input = params[:cel]
  @c = input.to_i
  

  The String input is then converted to the integer @c.
   
• The file config/routes.rb contains the line
  

  get "/convert/show"
  

  It specifies the route with controller = convert, action = show, and method = get as a named route.
   
• Recall that the HTTP verb GET is used to retrieve a web page when the user types the URL into a browser, or as the target page to retrieve with a hyperlink.
   
• However, when Rails uses HTTP to send data back to the server to be processed by the controller, the POST verb is used.
   
• To allow the POST verb to be used for sending the contents of :celsius back to the controller temp_version using the action convert, add this line to config/routes.rb:
  

  post "/convert/show"
  

• Practice Problem:   Convert the TemperatureDescriptors Example (Example 18) to a Rails project that accepts the temperature in a textfield and then shows the descriptor on the view. Modify the Ruby code of Example 18 to work in the controller.

The Array Class

• An array is a Ruby object that contains other ruby objects.
   
• Look at the Array Class UML Diagram.
   
• Three ways to create and populate an Array object:
  

  # Use the new method to create an empty array.
  # Use the << method to append items to the array.
  pets = Array.new
  pets << 'dog'
  pets << 'cat'
  pets << 'parrot'
  pets << 'goldfish'
  
  # Use the shortcut method:
  pets = ['dog', 'cat', 'parrot', 'goldfish']
  
  # Use the new method with a multiplication factor:
  a = Array.new(3, 'dog')
  

• Question: what is the value of pets[2]? Hint: an array starts counting its objects at the left with zero.
   
  Ans: It is 'parrot'. The indices always start counting with 0 from the left: a[0] is 'dog', a[1] is 'cat', a[2] is 'parrot', and a[3] is 'goldfish'.
   
• An array is used in a Rails website to hold resources that are retrieved from or inserted into a database table.

Project 5

• Example 24 (OnlineQuiz I Example)
   
• Discuss Project 5.