To Projects

One-many Relationships Tutorial

1. Choose two models that are related by a one-many relationship. For example: one student can have many awards (in high school). Student is the primary model; award is the dependent model. Do not choose students and awards for your final project.
    
   
2. Choose appropriate fields for each model.
    
   Example:
    
   

   Student last_name string first_name string birth_date date gpa float

   Award name string year integer student_id integer

   
   Each of the models automatially contains an id, which is the primary key. The foreign key student_id refers to id in the primary model.
    
3. Use the scaffold software to implement the Rails models, controllers, and views for the two model designs in 2.
    
   Example:   create a rails project named School. Then enter these two commands:
   

   rails g scaffold Student first_name:string 
       last_name:string birth_date:date gpa:float
   
   rails g scaffold Award name:string year:integer 
       student_id:integer
   

4. Establish a one-many relationship between the primary and dependent models:
    
   
   1. In app/models/student.rb, add these lines inside the class definition:
      

      # A student can have many awards.
      has_many :awards
      

   2. In app/models/award.rb, add these lines inside the class definition:
      

      # Each award is linked to a student through 
      # the student_id field.
      belongs_to :student
      

5. Run rake to create the database tables.
   

   rake db:migrate
   

6. Test your projects by starting the server and using these URLs:
   

   http://localhost:3000/students
   
   http://localhost:3000/awards
   

7. Write a helper method that will be used in Part 8. It will construct the student name by concatenating first_name and last_name. In app/models/student.rb, add this method definition:
   

   def name
       return first_name + " " + last_name
   end
   

8. The awards form _form.html.erb is difficult to use, because it requires knowledge of the student id field to create a new award. Replace the id text field in the dependent model with a more helpful dropdown menu.
    
   Example:   Replace the following code in app/views/awards/_form.html.erb
   

   <%= f.label :student_id %><br />
   <%= f.text_field :student_id %>
   

   with this code:

   Student Name<br />
   <%= f.select :student_id, @options %>
   

   Add this code to both of the new and edit methods in the awards controller (app/controllers/awards_controller.rb). Add it immediately after
   

   @award = Award.new
   

   in the new method and immediately after
   

   @award = Award.find(params[:id])
   

   in the edit method.
   

   @options = Student.find(:all, 
      :order => "last_name, first_name").
      collect do |s|
         [s.name, s.id]
      end
   

9. The index view for awards lists the student_id for each award. A more user friendly display would list the name instead. In the index view for the dependent model, replace the line
   

   <td><%= award.student_id %></td>
   

   with the line

   <td><%= award.student.name %></td>
   

10. In the show view for each item of the primary model, also show all of the associated dependent items.
     
    Example:   On the show view for student, write a loop that lists all of that student's awards. Add this code to apps/views/students/show.html.erb:
    

    <h3>Awards</h3>
    <table>
    <tr> 
        <th>Name</th>  
        <th>Year</th>  
        <th>Student</th> 
    </tr>
    
    <% @student.awards.each do |award| %>
    <tr>
        <td><%= award.name %></td>
        <td><%= award.year %></td>
        <td><%= award.student.name %></td>
    </tr>
    <% end %>
    </table>    
    

    
     
    
11. On the index view for student (file: app/views/students/index.html.erb) add a column Award Count that shows the number of awards for each student. Use this code to display the count:
    

    <%= student.awards.count %>
    

12. On the index page for the primary model, add a link to the index page for the dependent model.
     
    Example:   On the index view for students, add this link tag to the index view for awards:

    <p><%= link_to 'Awards', awards_path %></p>
    

    See the document Scaffold Generated RESTful Routes for more details.
     
13. On the index page for the dependent model, add a link to the index page for the primary model. See the previous step for an example.
     
14. Modify the CSS stylesheet of your project to make the fonts and colors more interesting and/or attractive.