Using join tables in ruby on rails

Everything true what @Jordan said, here the concrete steps to take:

1. Create a migration: rails g model CourseStudent creates a join model for the n:m relation, and the migration to the corresponding table.

2. Edit the migration file CreateCourseStudent so it contains the following:

   class CreateCourseStudent < ActiveRecord::Migration
     def change
       create_table :course_students do |t|
   
         # Your code comes here
         t.integer :student_id
         t.integer :course_id
   
         # Here comes the generated code 
         t.timestamps
       end
     end
   end
   

3. Run the migration: rake db:migrate. As a result, the join table should now exist in your database.

4. Add to the models the following code

   class Course < ActiveRecord::Base
     has_many :course_students
     has_many :students, :through => :course_students
   end
   
   class Student < ActiveRecord::Base
     has_many :course_students
     has_many :courses, :through => :course_students
   end
   
   class CourseStudent < ActiveRecord::Base
     belongs_to :student
     belongs_to :course
   end
   

You are now able to use the methods generated by the methods belongs_to and has_many:

• @course.students
• @student.courses

Try to find all the relevant facts and snippets in the Rails Guides, there you should find all information you need to get on track. Good luck!

This is an old question, but just in case anyone stumbles upon this like I did, you can now have the relationships has_and_belongs_to_many. So yes, you would create a join table:

create_join_table :students, :courses do |t|
  t.integer :student_id
  t.integer :course_id
end

And then in the models, you would say that a student has_and_belongs_to_many :courses And a course has_and_belongs_to_many :students. There is no need to make a third class called CourseStudent. This link has all this information