how to validate associated model id?

Question

I have a student and a course model. Student belongs to course, and course has many students.

class Student < ActiveRecord::Base
  attr_accessible :course_id,         


        

Answer 1

You can just do a custom validation method that checks the validity of your course id:

# course.rb
validates :course_id_is_valid

def course_id_is_valid
  if #course id isn't valid
    errors.add(:course_id, "is invalid")
  end
end

Alternately, if the course list is a discrete list, you can use the :in option on validations:

# course.rb
validates :course_id, :inclusion => { :in => list_of_courses, :message => "%{value} is not a course id" }

There are more options. Both of these examples come from the Rails docs:

http://guides.rubyonrails.org/active_record_validations_callbacks.html#custom-methods