8 files changed, 22 insertions, 2 deletions
diff --git a/activerecord/CHANGELOG b/activerecord/CHANGELOG
index 433ec57e23..eca074f324 100644
--- a/activerecord/CHANGELOG
+++ b/activerecord/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Fix that has_many :through honors the foreign key set by the belongs_to association in the join model (closes #4259) [andylien@gmail.com / Rick]
+
 * SQL Server adapter gets some love #4298 [rtomayko@gmail.com]
 
 * Added OpenBase database adapter that builds on top of the http://www.spice-of-life.net/ruby-openbase/ driver. All functionality except LIMIT/OFFSET is supported #3528 [derrickspell@cdmplus.com]
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index e242b9f7a1..3d3d53c677 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -65,14 +65,17 @@ module ActiveRecord
             raise ActiveRecordError, "Could not find the association '#{@reflection.options[:through]}' in model #{@reflection.klass}"
           end
           
+          # Get the actual primary key of the belongs_to association that the reflection is going through
+          source_primary_key = through_reflection.klass.reflect_on_association(@reflection.name.to_s.singularize.to_sym).primary_key_name
+          
           if through_reflection.options[:as]
             conditions = 
-              "#{@reflection.table_name}.#{@reflection.klass.primary_key} = #{through_reflection.table_name}.#{@reflection.klass.to_s.foreign_key} " +
+              "#{@reflection.table_name}.#{@reflection.klass.primary_key} = #{through_reflection.table_name}.#{source_primary_key} " +
               "AND #{through_reflection.table_name}.#{through_reflection.options[:as]}_id = #{@owner.quoted_id} " + 
               "AND #{through_reflection.table_name}.#{through_reflection.options[:as]}_type = #{@owner.class.quote @owner.class.base_class.name.to_s}"
           else
             conditions = 
-              "#{@reflection.klass.table_name}.#{@reflection.klass.primary_key} = #{through_reflection.table_name}.#{@reflection.klass.to_s.foreign_key} " +
+              "#{@reflection.klass.table_name}.#{@reflection.klass.primary_key} = #{through_reflection.table_name}.#{source_primary_key} " +
               "AND #{through_reflection.table_name}.#{through_reflection.primary_key_name} = #{@owner.quoted_id}"
           end
           
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index e54e38e184..e56682ec92 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -140,6 +140,10 @@ module ActiveRecord
         end
       end
 
+      def through_reflection
+        @through_reflection ||= options[:through] ? active_record.reflect_on_association(options[:through]) : false
+      end
+
       private
         def name_to_class_name(name)
           if name =~ /::/
@@ -147,6 +151,8 @@ module ActiveRecord
           else
             if options[:class_name]
               options[:class_name]
+            elsif through_reflection # get the class_name of the belongs_to association of the through reflection
+              through_reflection.klass.reflect_on_association(name.to_s.singularize.to_sym).class_name
             else
               class_name = name.to_s.camelize
               class_name = class_name.singularize if [ :has_many, :has_and_belongs_to_many ].include?(macro)
diff --git a/activerecord/test/associations_join_model_test.rb b/activerecord/test/associations_join_model_test.rb
index 7395aa5739..79ac19ec61 100644
--- a/activerecord/test/associations_join_model_test.rb
+++ b/activerecord/test/associations_join_model_test.rb
@@ -39,6 +39,11 @@ class AssociationsJoinModelTest < Test::Unit::TestCase
     assert_equal tags(:general), posts(:welcome).tags.first
   end
 
+  def test_polymorphic_has_many_going_through_join_model_with_custom_foreign_key
+    assert_equal tags(:misc), taggings(:welcome_general).super_tag
+    assert_equal tags(:misc), posts(:welcome).super_tags.first
+  end
+
   def test_polymorphic_has_many_create_model_with_inheritance_and_custom_base_class
     post = SubStiPost.create :title => 'SubStiPost', :body => 'SubStiPost body'
     assert_instance_of SubStiPost, post
diff --git a/activerecord/test/fixtures/db_definitions/schema.rb b/activerecord/test/fixtures/db_definitions/schema.rb
index 53aa7c1967..efe9cb35ab 100644
--- a/activerecord/test/fixtures/db_definitions/schema.rb
+++ b/activerecord/test/fixtures/db_definitions/schema.rb
@@ -2,6 +2,7 @@ ActiveRecord::Schema.define do
 
   create_table :taggings, :force => true do |t|
     t.column :tag_id, :integer
+    t.column :super_tag_id, :integer
     t.column :taggable_type, :string
     t.column :taggable_id, :integer
   end
diff --git a/activerecord/test/fixtures/post.rb b/activerecord/test/fixtures/post.rb
index a00fd80671..9456582729 100644
--- a/activerecord/test/fixtures/post.rb
+++ b/activerecord/test/fixtures/post.rb
@@ -22,6 +22,7 @@ class Post < ActiveRecord::Base
 
   has_many :taggings, :as => :taggable
   has_many :tags, :through => :taggings
+  has_many :super_tags, :through => :taggings
 
   has_one :tagging, :as => :taggable
 
diff --git a/activerecord/test/fixtures/tagging.rb b/activerecord/test/fixtures/tagging.rb
index 8bc844c370..4d3878933a 100644
--- a/activerecord/test/fixtures/tagging.rb
+++ b/activerecord/test/fixtures/tagging.rb
@@ -1,4 +1,5 @@
 class Tagging < ActiveRecord::Base
   belongs_to :tag
+  belongs_to :super_tag, :class_name => 'Tag', :foreign_key => 'super_tag_id'
   belongs_to :taggable, :polymorphic => true, :counter_cache => true
 end
 \ No newline at end of file
diff --git a/activerecord/test/fixtures/taggings.yml b/activerecord/test/fixtures/taggings.yml
index 38ec1ba5b1..617210d604 100644
--- a/activerecord/test/fixtures/taggings.yml
+++ b/activerecord/test/fixtures/taggings.yml
@@ -1,6 +1,7 @@
 welcome_general:
   id: 1
   tag_id: 1
+  super_tag_id: 2
   taggable_id: 1
   taggable_type: Post