validation.rb

module ActiveRecord
  module PreventChangeCloseAcademicYearDependents
    def self.included(base)
      base.before_destroy :validate
      base.validate :validate, :on => :update
    end

    def validate
      if (respond_to? :academic_year) && (academic_year_is_closed?)
        errors.add(:base, :academic_year_is_closed)
      end
    end

    private

    def academic_year_is_closed?(academic_year_repository = AcademicYear)
      academic_year_repository.find(academic_year.id).closed?
    end
  end
end