multiple foreign keys in one table reference the same table column

Here is my table structure:

keyterms: id, key_word, primary key (id) user_keywords: id, user_id, expertise_keyterm_id, partners_keyterm_id, primary key(id), foreign key(expertise_keyterm_id), foreign key(partners_keyterm_id)

In UserKeyword model: class UserKeyword < ActiveRecord::Base   belongs_to :users, :class_name=>'User', :foreign_key => :user_id   belongs_to :keyterms, :class_name=> "Keyterm", :foreign_key => :expertise_keyterm_id   belongs_to :keyterms_expertise, :class_name=> "Keyterm", :foreign_key => :expertise_keyterm_id end

In Keyterm model: class Keyterm < ActiveRecord::Base   has_many :user_keywords, :class_name => 'UserKeyword' end

In users controller def myfunction   @user = User.find(params[:id])   render :xml =>@user.to_xml(:include=>{ :user_keywords=>{:include=> :keyterms}}) end

But on the xml page, only expertise_keyterm shows up, parterner keyterm doesn't and I am using rails 3.0.9. Could anyone help me? Thanks,