app/models/checklist_topics_check.rb
class ChecklistTopicsCheck < ActiveRecord::Base
attr_accessible :ordering, :value, :unchecked_value
belongs_to :check, class_name: 'ChecklistCheck', :foreign_key => 'checklist_check_id'
belongs_to :topic, class_name: 'ChecklistTopic', :foreign_key => 'checklist_topic_id'
default_scope :order => "checklist_topics_checks.ordering"
end