To Lecture Notes

IT 232 -- 10/5/15

Review Exercises

1. Here is the correct validation that uses a regular expression to check the input:
   

   validates :phone, format: { with: /\A\d{3}\/\d{3}-\d{4}\Z/ }

   Write and test a validation that checks a part number which has the format
   

   (A|B|C)\d\d\d-(D|E|F)\d\d\d\d\d
   Ans:
   validates :part_num, format: { with /\A(A|B|C)\d{3}-(D|E|F)\d{5}\Z/ }
   

2. What do these acronymns mean?
   

   DRY  CoC  CRUD  HTTP  REST
   

   Ans: DRY: Don't Repeat Yourself; CoC: Convention over Configuration; CRUD: The standard database operations Create, Read, Update, Destroy; HTTP: Hypertest Transfer Protocol; REST: Representation State Transfer.
3. What are some HTTP methods (also called verbs)?
   Ans: GET HEAD POST PUT DELETE
4. Try getting a webpage using old fashioned HTTP:
   

   telnet condor.depaul.edu 80
   GET /sjost/ HTTP
   

5. What is the difference between the HTTP verbs GET and POST for sending a form back to the server?
6. What is the difference between FormTagHelper and FormTag methods?
   Ans: When sending a form back to the server, GET embeds the data in the URL to send it, for example:
   

   http://localhost:3000/client_server/server?utf8=%E2%9C%93 ⇓
       &name=Alice&gender=F&age=11&commit=Submit+Info+to+Server
   

7. The Rails BlogPostSite Example project contains source code errors. There are about 5 errors for the index and show views and the _form.html.erb file.  There are about 2 errors on the new and edit views. Find the errors.
8. The TemperatureConverter1 Example project contains source code errors (about 5 errors per page). Find the errors.
9. Modify the Temperature1 project to:
   
   1. include another textfield on the input view for entering a name,
   2. enter the name, the Celsius temperature, and the Fahrenheit temperature in a database table with model name TempConvertRecord

Project 3

• Look at the Project 3 Description.

Many-to-many Relationships

• Here are some examples of many relationships:
  
       A student takes many classes; a class is taken by many students.
  
       A person belongs to many organizations; an organization has many members.
  
       An actor works in many movies (over his or her career); a movie employees many actors.
  
       (Project 3) A user likes many photos; a photo is liked my many users.
  
       (Facebook) A person has many friends.
• In Rails, a many-to-many relationship can be implemented with one of three methods:
  
  1. Models A and B are related with a many-to-many relationship if a third model C contains fields a_id and b_id. The model files for A and B have has_many :cs; the model file for C has belongs_to :a and belongs_to :b. The rows of C determine which rows of A and B are related.
     Example: In the School1 Example, Student and Course are related through the model Enrollment.
  2. Don't use a third model, but instead use a migration to create a new table named as_bs that connects the models A and B.  The model A contains has_and_belongs_to_many :as; the model B contains has_and_belongs_to_many :bs.
     Example: In the School2 Example, Student and Course are related through the table courses_students (courses and students must be listed in alphabetical order.
  3. Use a third model, but use has_and_belongs_to_many statements. This combines the best of both worlds from methods 1 and 2.
• Look at the School1 and School2 Examples.