added :piggyback option to has_many :through relationships to pick up values from the join table as needed

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3323 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

2 files changed, 5 insertions, 1 deletions

diff --git a/activerecord/test/associations_join_model_test.rb b/activerecord/test/associations_join_model_test.rb
index d53a8d98d3..502e4d28c5 100644
--- a/activerecord/test/associations_join_model_test.rb
+++ b/activerecord/test/associations_join_model_test.rb
@@ -38,5 +38,9 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
   def test_polymorphic_has_many_going_through_join_model_with_inheritance
     assert_equal tags(:general), posts(:thinking).tags.first
   end
+  
+  def test_has_many_with_piggyback
+    assert_equal "2", categories(:sti_test).authors.first.post_id
+  end
     
 end
diff --git a/activerecord/test/fixtures/category.rb b/activerecord/test/fixtures/category.rb
index 01938d1405..d0e0dfb770 100644
--- a/activerecord/test/fixtures/category.rb
+++ b/activerecord/test/fixtures/category.rb
@@ -6,7 +6,7 @@ class Category < ActiveRecord::Base
   end
   
   has_many :categorizations
-  has_many :authors, :through => :categorizations  
+  has_many :authors, :through => :categorizations, :piggyback => [:post_id]  
 end
 
 class SpecialCategory < Category