module Gaku
  class SemesterCourse < ActiveRecord::Base

    belongs_to :semester
    belongs_to :course

    validates :course_id, presence: true

    validates :semester_id,
              presence: true,
              uniqueness: {
                            scope: :course_id,
                            message: I18n.t(:'semester_course.uniqueness')
                          }

    def self.group_by_semester
      all.includes([:semester, :course]).group_by(&:semester_id)
    end

  end
end