To Lecture Notes

IT 232 -- 10/28/15

Review Exercises

1. What is a session variable?
   Ans: A session variable stores information that persists through multiple HTTP page gets and posts.
2. How do you store data into and retrieve data from a session variable? Ans:
   

   # To store:
   session[:key] = the_info
   # To retrieve:
   x = session[:key]
   

3. How long does the information in the session variable last?
   Ans: Until all browser windows are closed or until the reset_session method is called.
4. Where is the session variable data stored?
   Ans: In cookies on the user's harddrive.
5. Create a Rails project named TestSession, a non-scaffold-based controller named SecretMessage, and three views that do the following:
   
   1. view1: stores a secret message in the session variable,
   2. view2: displays the secret message from the session variable.
   Ans: Here is the source code for the TestSession project.
6. What is a digest?
   Ans: It is a one-way encryption algorithm. For example, the MD5 digest algorithm always encodes a message (which could be a password) in 32 bytes. A digest as also called a cryptographic hash.
7. True or false: if a password is encrypted with MD5, the original password can be obtained if the hacker can obtain the private key.
   Ans: False. A digest is a one-way encryption algorithm. There is no private key that can decode it.
8. Genius Question: For Project 4, how can you take all of the photos from all followers of a user and display them together or order of most recent to least recent.
   Ans: See the MiniTwitter Example.

The CustomLogin Example

• Study the source code from the CustomLogin Example.

The EmployeeRoster Example

• Look at the EmployeeRoster Example.
• This example shows how create a self referential join. A one-to-many relationship from the employee relationship to itself creates the methods manager and subordinate.
• This concept can apply to the connections in the LinkedIn network.  However, for LinkedIn, the connections are bidirectional: belongs_to is the only method that is needed in the model.

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.

Handling Validation Errors in a Non-scaffold-based Controller

• A flash variable is similar to a session variable.
• A session variable retains its information until all browser windows are closed or until the reset_session method is called.
• A flash variable retains its information only for the next view that is displayed by the browser.
• Look at the School2 Example.