has_many :through

[skg]

I have the 3 tables

1)service_desk_tickets

id integer not null default
nextval('public.service_desk_tickets_id_seq':
:text)
number character varying(15)
title character varying(100)
service_desk_status_id integer
etc.....

2)cis

id integer not null default nextval('public.cis_id_seq'::text)
citype character varying(30)
ci_number character varying(15)
content_id integer
etc....

3)service_desk_cis(This is a junction table)

id integer not null default nextval('public.service_desk_cis_id_se
q'::text)
service_desk_ticket_id integer
ci_id integer
service_desk_ci_association_type_id integer

Associations as
In service_desk_ticket.rb

has_many :service_desk_cis
has_many :cis, :through => :service_desk_cis

In ci.rb
has_many :service_desk_cis
has_many :service_desk_tickets, :through => :service_desk_cis

in service_desk_cis.rb

belongs_to :service_desk_ticket
belongs_to :ci

In controller
@sd_cis=ServiceDeskTicket.find(params[:id]).cis (This is working)

MY PROBLEM IS HOW TO GET service_desk_ci_association_type_id

Please help
Sijo