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IT 231 -- 8/8/12

Review Questions

1. What is the Rails FormTagHelper method used to create for each of these HTML items?
    
   
   Form    Text field    Submit Button
   
   Ans: The FormTagHelper methods are form_tag, text_field_tag, and submit_tag, respectively.
    
2. Find the mistakes if the desired action is play_song:
   

   <% formtag :play_song =>
   <@= textfield_tag :n_verses, 99, @> ><br />
   <% submit-tag :play_song, Play Song, ><br />
   <%= end %>
   
   Corrected version:
   
   <%= form_tag 'play_song' %>
   <%= text_field_tag :n_verses, 99 %> ><br />
   <% submit_tag 'Play Song' ><br />
   <% end %>
   

3. Find the mistakes in this controller statement:
   

   celsius_temp = param ( : fahr ).toInteger
   
   Corrected version:
   
   celsius_temp = params[:fahr].to_i
   

4. What is the hex color code for each of these colors:
    
   
   maroon    olive    silver    teal    yellow
   
   Ans: See this chart of Standard HTML Color Names and Corresponding Hex Color Codes.
    
5. Convert the color code to hex.
   

   body { background-color: rgb(30,135,214); }
   
   Ans:
   
   body { background-color: #1e87e6; }
   

6. Convert the color code to decimal.
   

   body { background-color: #40abef; }
   
   Ans:
   
   body { background-color: rgb(64, 171, 238); }
   

7. Which is the larger hex value in each pair?
   

   54 82    6d 69    a3 da    a9 9a
   
   Ans: 
   
   54 < 82    6d > 69    a3 < da    a9 > 9a
   

8. Add more blue to the color in Problem 6.
    
   Ans: For example, change the blue color component ef to f4.

Project 6

• Project 6 saves the answers to an online survey in a database table.
   
• Use Rails FormHelper methods to create controls that are each linked to the corresponding database table field.
   
• Like the Rails scaffold statement, a model statement creates the the database design file and associated helper methods for accessing the database. As usual, call rake db:migrate to actually create the database.
   
• Unlike the Rails scaffold statement, generating a model does not write any HTML or CSS code. You must implement the views, layouts, and style file yourself.
   
• See Examples 28 and 29 (OnlineQuiz and CreditCard examples). Use these examples as a models for Project 6.

FormHelper vs. FormTagHelper Methods

• Use FormHelper methods when you are using a form to edit a row in a database, or to add a new row to the database.
   
• Use FormTagHelper methods when the piece of data you are inputing does not directly correspond to any field in the database.
   
• FormHelper methods process an entire database row at a time; FormTagHelper methods process separately each piece of data coming from or going to a control.
   
• References:
   
  api.rubyonrails.org/classes/ActionView/Helpers/FormTagHelper.html
   
  api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html
   
  
  1. Form
      
     FormTagHelper Version:
     

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

  FormHelper Version:
  

  <% form_for @item, :url => { :action => 'show' } do |f| %>
  ... Controls go here.
  <% end %>
  

  2. Textfield
      
     FormTagHelper Version:
     

     <%= text_field_tag :celsius, '20', :class => 'tf' %>
     

     :celsius is the name; '20' is the initial value.
      
     FormHelper Version:
     

     <%= f.text_field :celsius, :class => 'tf' %>
     

     :celsius is the field of the database object f.
      
  3. Dropdown Menu
      
     FormTagHelper Version:
      
     

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

     :source_rate is the name; the first column of the array are the values displayed in the dropdown menu; the second column are the values returned to the controller to be read by a params statement. the option tags are the HTML option tags.
     
      
     FormHelper Version:
     

     <%= f.select_tag :source_rate, 
          [['Dollars', 1.00000],
           ['Euro', 1.36749],
           ['Pesos', 12.6149],
           ['Pounds', 1.58228]],
          :class => 'ddm'
     

     :source_rate is the field of the database object f; the values of the dropdown menu are specified in the array as they were in the FormTagHelper version; note that for the FormHelper version, no options_for_select method is needed.
      
  4. Radio Button
      
     FormTagHelper Version:
     

     <%= 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 to be read by a params statement
     true means that the radio button should be initially checked.
      
     FormHelper Version:
     

     <%= f.radio_button :group, value, :checked => 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 to be read by a params statement
     :checked => true means that the radio button should be initially checked.
      
  5. CheckBox
     
      
     FormTagHelper Version:
     

     <%= check_box_tag :sugar, 1, true, :class => 'cb' %>
     

     :sugar is the name of the checkbox
     1 is the value returned to the controller in a params statement
     false means that the checkbox is initially checked.
      
     FormHelper Version:
     

     <%= f.check_box :sugar, 1, :checked => true, :class => 'cb' %>
     

     :sugar is the name of the checkbox
     1 is the value returned to the controller in a params statement, 0 will be returned if the box is not checked.
     :checked => true means that the checkbox is initially checked.

Examples of Forms Using FormHelper Methods

• See Example 28 and 29 (OnlineQuiz and CreditCard examples). Use these examples as a models for Project 6.
   
• Build Example 27 (FindGradeData Example).

The Range Class

• Look at the Range Class UML Diagram.
   
• Two ways to create a new Range object.
  

  # 1. Create a range that includes the end using new method.
  r = Range.new(1, 5)
  
  # 2. Shortcut to create a range that includes the end.
  r = 1..5
  

• Write code that tests some of the methods of the Range class in the UML diagram.
   
• Ruby code that tests the VendingMachine class using a nested for statement with ranges:
  

  vm = VendingMachine.new
  (1..6).each do |i|
     (1..3).each do |j|
        vm.deposit_quarter
     end
     vm.select_candy
  end
  

Migrations

• Create a Rails model named Student with the fields name:string, student_id:integer, gpa:float. Then do the following:
   
  
  1. Add a new field gender:string.
     

     rails g migration AddGenderToStudents gender:string
     

  2. Remove the field gpa.

  rails g migration RemoveGpaFromStudents gpa:float
  

  3. Look at the migration class files generated in the db/migrations folder.
      
  4. A migration class usually has an up method that is executed when the migration is executed with rake db:migrate; it also generally has a down method that is executed with rake db:rollback.
      
  5. Type rake db:migrate to execute the migration.
      
  6. Type rake db:rollback to rollback the migration to the state before the previous db:migrate was executed.
      
  7. Each migration class file has a number that specifies the order in which migrations are executed.

Another Project with a One-to-many Relationship

• Build Example 32 (PetSalon Example).