To Lecture Notes

IT 232 -- 10/7/15

Review Exercises

Use these documents to help you with the review exercises:
     FormTagHelper vs. FormHelper Methods
     ActiveRecord Queries

1. Write a form tag with, action confirmation in the controller deposit. Ans:
   

   <%= form_tag 'confirmation' do %>
   

   or

   <%= form_tag deposit_confirmation_path do %>
   

2. Write a textfield tag with name ssn, initial value Enter SSN, and CSS class ctrl. Ans:
   

   <%= text_field_tag :ssn, 'Enter SSN', class: 'ctrl' %>

3. Write a submit tag with caption Submit Data and CSS class ctrl. Ans:
   

   <%= submit_tag 'Submit Data', class: 'ctrl' %>

4. Modify the TemperatureConverter1 project to:
   
   1. include another textfield on the input view for entering a name,
   2. when the submit button is clocked, enter the name, the Celsius temperature, and the Fahrenheit temperature in a database table with model name TempConvertRecord
   3. display the records in the database on the display page.
   Ans: See the TemperatureConverter2 Example.

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.

  students id name gender phone 1 Alice F 222/333-4444 2 Scott M 555/666-7777 3 Janine F 888/999-3333

  courses id course_num title credit_hours 1 IT130 Intro to Web Programming 4 2 ENG101 College Writing 3 3 CHEM205 Organic Chemistry 4 4 ENG390 Senior Seminar 2

  enrollments
  id	course_id	student_id
  1	3	1
  2	2	2
  3	1	3
  4	4	2
  5	1	3

  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_many with the through option. This was an A object has access to the collection of B objects to which it is related, and vice versa.
• Look at the School1 and School2 Examples.

A Modification to the School1 Example

1. In the School1 Example, replace the dropdown list in the Student show view with radio buttons.
   Ans: Replace this dropdown menu code in the Student show view
   

   <%= select_tag(:course,
         options_from_collection_for_select(
             @student.unenrolled_courses, :id, :course_num)) %>
     
   

   with this code that creates radio buttons:
   

    <% @student.unenrolled_courses.each do |course| %>
     <%= radio_button_tag(:course, course.id, checked: false) %> 
                                        <%= course.course_num %><br> 
   <% end %>
   

Project 3

• Discuss Project 3 in groups of 3 or 4. Discuss how to implement Project 3 and what further information you need to do so.