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 should look into creating a custom validation method:

class Student < ActiveRecord::Base
  validates :course_id, presence: true, numericality: { only_integer: true }
  ...
  validate :validate_course_id

private

  def validate_course_id
    errors.add(:course_id, "is invalid") unless Course.exists?(self.course_id)
  end
end

First, your model will make sure that the course_id is a valid integer, and then your custom validation will make sure that the course exists in the database.