To Lecture Notes

IT 231 -- 10/4/12

Review Questions

1. What is the difference between the Rails generate scaffold statement and the Rails generate model statement?
   Ans: The Rails generate scaffold statement creates a new database table together with a controller and the views index, show, new, and edit. The Rails generate model statement only creates the new database table.
    
2. Write a Ruby line that prints a random number from 0 to 10 with equal probability.
   

   print rand(11)
   

3. Write a Ruby line that assigns to employee_id, a random number 1001 to 1999 with equal probability.
   

   employee_id = 1001 + rand(999)
   print employee_id, "\n"
   

4. Modify Example 17 (Overtime Example) to receive input from the keyboard.
   Ans: Replace the statements
   

   hours_worked = 45.0
   hourly_salary = 10.0
   

   by
   

   print "Enter hours worked: "
   hours_worked = STDIN.gets.chomp.to_f 
   print "Enter hourly salary: "
   hourly_salary = STDIN.gets.chomp.to_f 
   

5. Modify Example 19 (ConsultantBSGenerator Example) to display its output in a rails view.
    
   Ans: Put all of this code in the code in the controller. Replace the last statement
   

   puts "Our consultants can help your company " +
       verb + " " + adjective + " " + noun + "."
   

   with
   

   @sentence = "Our consultants can help your company " +
       verb + " " + adjective + " " + noun + "."
   

   Put this code in the view:
   

   <%= @sentence %>
   

6. Write a Rails application with a view that randomly displays two of these dice. Also display the sum of the dice.
    
   
   1.jpg   2.jpg   3.jpg   4.jpg   5.jpg   6.jpg
   
   Use three instance variables @die1, @die2, and @sum, whose values are set in the controller.
   Ans: Create a Rails project named Casino with controller RollDice and view display. Put this method in the controller
   

   def display
     roll1 = 1 + rand(6)  
     roll2 = 1 + rand(6)  
     @die1 = roll1.to_s + ".jpg"
     @die2 = roll2.to_s + ".jpg"
     @sum = roll1 + roll2
   end
   

   and this code in the display view
   

   <p><%= image_tag @die1 
          image_tag @die1 %></p>
   
   <p>The sum of the rolls is <%= @sum %></p>
   

Some ActiveRecord Method Calls

• Create a Rails project named GroceryStore. Create a model named GroceryItem having fields code, description, price, and on_sale.
   
• Run rake to create the database and the database table.
   
• Add one grodery item to the table using ActiveRecord method calls.
   
• Copy this Ruby seed code into the seed file, located at db/seeds.rb.
   
• Run the seed file like this:
  

  > rake db:seed
  

• Try out these ActiveRecord method calls for the model Student in the Rails console:
  

  # Return the first record in the table.
  GroceryItem.first
  
  # Return the last record in the table.
  GroceryItem.last
  
  # Return number of rows in table.
  GroceryItem.count
  
  # Get grocery_item with id=3
  s = GroceryItem.find(3)
  
  # Get grocery_item with code=44444, using dynamic finder method
  s = GroceryItemStudent.find_by_code(44444)
  
  # Get grocery_item with description "Green Beans".
  s = GroceryItem.find_by_description("Green Beans")
  
  # Get all grocery items for which on_sale is true.
  s = GroceryItem.find_all_by_on_sale(true)
  

• Later we will see how to retrieve and process an array of objects from the database table.

Modifying Images with Image Editing Software

• Resizing an image with MS Paint
   
  
  Right Click on image name in MS Explorer >> Select open with Paint. MS-Paint will open. Select Resize Image >> Set the horizontal and vertical boxes to a percentage less than 100 to shrink the image. Save the image.
  
  
• Cropping an image with MS Paint  
   
  
  Right Click on image name in MS Explorer >> Select open with >> paint. MS-Paint will open. Click the Select Button >> Use the mouse to select the rectangular area of the image to keep >> Click the crop button. Save the image.
  
  
• Lightening an image with Adobe Photoshop  
   
  
  Invoke Adobe Photoshop. Select File >> Open >> Browse to desired imaage. Select Image >> Adjustments >> Hue-saturation. Move the Lightness slider to the right. Click OK. Save the image.
  
  

Project 4

• Look at the Flintstones1 and Flintstones2 Examples (Example 22 and 22.5).
   
• Look at Project 4.

Practice Problems

1. Write a Ruby script that inputs the course score and outputs the course grade.
   A == 90..100, B == 80..89, C == 70..79, D == 60..69, F == 0..59.
    
2. Add this method to the Dice class (Example 14) and test it:
   

   def doubles?
       if @die1 == @die2
           return true
       else
           return false
       end
   end
   

   
   
3. Create a Rails project named TestProject. Then do the following:
    
   
   1. Generate a controller named ShowInfo with one action home.
   2. Add another action named page1.
   3. Define titles in the controller for the views.
   4. Add a stylesheet that
      • sets the background color to silver
      • the text color to maroon
      • the font family to Arial
      • the hyperlinks (link_to) to yellow
      • the size of the h1 tag to 50% larger than the body text
   5. Add a layout page that is compatible with the views.