To Lecture Notes

IT 232 -- 10/26/15

Review Exercises

1. How do you set a background image for a controller?
   
   Ans: Put this line in the controller SCSS stylesheet:
   

   body { background-image: url(image.jpg); }
   

2. How do you designate a view as the home page to be displayed with http://localhost:3000.
   Ans: To set the index page of the Student controller as the home page, put this line in the routes file:
   

   root 'students#index'
   

   To set the show page with id=7 as the root node:
   

   root 'students#show', id: '7'
   

3. What are the steps to adding a new page to an existing controller?
   Ans: If the new view directory is to be added to the students controller,
   
   1. add the new ERB file directory.html.erb to the views folder,
   2. add a new method named directory to the students controller,
   3. add this route to the routes file:
      

      resources :students do
        collection do
          get :directory
        end
      end
      

4. What are the path names for a scaffold-based controller with model name Student? Run rake routes to verify your answer. Ans:
   

   View	Helper Method
   index	students_path
   show	student_path(@student) or @student
   new	new_students
   edit	edit_student(@student)

   
   Here is the result of running rake routes:
   

         Prefix Verb   URI Pattern                  Controller#Action
       students GET    /students(.:format)          students#index
                POST   /students(.:format)          students#create
    new_student GET    /students/new(.:format)      students#new
   edit_student GET    /students/:id/edit(.:format) students#edit
        student GET    /students/:id(.:format)      students#show
                PATCH  /students/:id(.:format)      students#update
                PUT    /students/:id(.:format)      students#update
                DELETE /students/:id(.:format)      students#destroy
   

5. Translate the following FormTagHelper method calls into FormHelper method calls:
   

   a.   <%= form_tag convert_display_path do %>
   Ans: <%= form_for @conv_rec, url: convert_display_path do |f| %>
   
   b.   <%= text_field_tag :name %>
   Ans: <%= f.text_field :name %>
    
   c.   <%= submit_tag 'Submit Data' %>
   Ans: <%= f.submit 'Submit Data' %>
   

Examples from Last Week

• Look at the TemperatureConverter3 and BlogPostSite2 Examples.
• Here is a comparison of the source code for the TemperatureConverter2 and TemperatureConverter3 Examples:
• The BlogPostSite2 Example shows how to implement a basic login authentication system.

Project 4

• Look at the Project 4 Description.

Session Variables

• Because HTTP is a stateless technology, information on a webpage is not remembered by the server.
• Use session variables to remember information through multiple page gets or posts (in the HTTP sense).
• Session variable information is retained until that session variable is changed or reset.
• To set a Session variable:
  

  session[:key] = "Important information"
  

  (You choose the key.)
• To retrieve the information:
  

  info = session[:key]
  

• If you know what a Ruby Hash object is, that's what a session variable is.
• Look at the CustomLogin Example.
• In this example, a session variable is used to remember whether a user has logged in:

  session[:logged_in] = true
  

• What a user logs out, the session variables are reset with reset_session.

Digests

• A digest is a one-way encryption of a string.
• A digest is also called a cryptographic hash function or hash for short. This is different than a Ruby Hash object.
• An ideal digest has these properties:
  
  1. For any string, it is easy to compute the digest.
  2. Given the digest, it is infeasible to obtain the original string.
  3. It is infeasable to change the string without changing its digest.
  4. It is infeasable to find two different strings that have the same digest.
• A popular digest algorithm is SHA2.
• Look at the CustomLogin Example.
• Practice Problem: Modify the LoginInfo controller to allow a new user to enter a username and password and have the encrypted password entered into the login_infos table.

The Depot1 Example

• Implement the Depot1 project:
  

  Product:  cat_num  title  description  image_url  price
  Customer: last_name  first_name  address  cc_type  cc_num  cc_exp
  ShoppingCart: customer_id
  LineItem: product_id  shopping_cart_id  quantity
  

  Here are some images and a seed file for Product. See the Depot1 Example.

Photo Model Code

• In a standalone Ruby script, try reading an input file, converting it to uppercase, and writing back out to disc. Do this in three ways:
  
  1. Read, process, and write line at a time.
  2. Read, process, and write one character at a time.
  3. Read the entire file into a string, process it, and write this string.
• Discuss the Photo model code for the PetPhotoUpload Example.