fix assignment to has_one :through associations.

Signed-off-by: Michael Koziarski <michael@koziarski.com>

activerecord/lib/active_record/associations/has_one_through_association.rb

@@ -8,11 +8,10 @@ module ActiveRecord
         current_object = @owner.send(@reflection.through_reflection.name)
         
         if current_object
-          klass.destroy(current_object)
-          @owner.clear_association_cache
+          current_object.update_attributes(construct_join_attributes(new_value))
+        else
+          @owner.send(@reflection.through_reflection.name,  klass.send(:create, construct_join_attributes(new_value)))
         end
-        
-        @owner.send(@reflection.through_reflection.name,  klass.send(:create, construct_join_attributes(new_value)))
       end
       
     private

activerecord/test/cases/associations/has_one_through_associations_test.rb

@@ -3,9 +3,11 @@ require 'models/club'
 require 'models/member'
 require 'models/membership'
 require 'models/sponsor'
+require 'models/organization'
+require 'models/member_detail'
 
 class HasOneThroughAssociationsTest < ActiveRecord::TestCase
-  fixtures :members, :clubs, :memberships, :sponsors
+  fixtures :members, :clubs, :memberships, :sponsors, :organizations
   
   def setup
     @member = members(:groucho)
@@ -120,4 +122,40 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
     clubs(:moustache_club).send(:private_method)
     @member.club.send(:private_method)
   end
+
+  def test_assigning_to_has_one_through_preserves_decorated_join_record
+    @organization = organizations(:nsa)
+    assert_difference 'MemberDetail.count', 1 do
+      @member_detail = MemberDetail.new(:extra_data => 'Extra')
+      @member.member_detail = @member_detail
+      @member.organization = @organization
+    end
+    assert_equal @organization, @member.organization
+    assert @organization.members.include?(@member)
+    assert_equal 'Extra', @member.member_detail.extra_data
+  end
+
+  def test_reassigning_has_one_through
+    @organization = organizations(:nsa)
+    @new_organization = organizations(:discordians)
+
+    assert_difference 'MemberDetail.count', 1 do
+      @member_detail = MemberDetail.new(:extra_data => 'Extra')
+      @member.member_detail = @member_detail
+      @member.organization = @organization
+    end
+    assert_equal @organization, @member.organization
+    assert_equal 'Extra', @member.member_detail.extra_data
+    assert @organization.members.include?(@member)
+    assert !@new_organization.members.include?(@member)
+
+    assert_no_difference 'MemberDetail.count' do
+      @member.organization = @new_organization
+    end
+    assert_equal @new_organization, @member.organization
+    assert_equal 'Extra', @member.member_detail.extra_data
+    assert !@organization.members.include?(@member)
+    assert @new_organization.members.include?(@member)
+  end
+
 end

activerecord/test/fixtures/organizations.yml

@@ -0,0 +1,5 @@
+nsa:
+  name: No Such Agency
+discordians:
+  name: Discordians
+

activerecord/test/models/member.rb

@@ -6,4 +6,6 @@ class Member < ActiveRecord::Base
   has_one :favourite_club, :through => :memberships, :conditions => ["memberships.favourite = ?", true], :source => :club
   has_one :sponsor, :as => :sponsorable
   has_one :sponsor_club, :through => :sponsor
+  has_one :member_detail
+  has_one :organization, :through => :member_detail
 end

activerecord/test/models/member_detail.rb

@@ -0,0 +1,4 @@
+class MemberDetail < ActiveRecord::Base
+  belongs_to :member
+  belongs_to :organization
+end

activerecord/test/models/organization.rb

@@ -0,0 +1,4 @@
+class Organization < ActiveRecord::Base
+  has_many :member_details
+  has_many :members, :through => :member_details
+end

activerecord/test/schema/schema.rb

@@ -197,6 +197,12 @@ ActiveRecord::Schema.define do
     t.string :name
   end
 
+  create_table :member_details, :force => true do |t|
+    t.integer :member_id
+    t.integer :organization_id
+    t.string :extra_data
+  end
+
   create_table :memberships, :force => true do |t|
     t.datetime :joined_on
     t.integer :club_id, :member_id
@@ -249,6 +255,10 @@ ActiveRecord::Schema.define do
     t.integer :shipping_customer_id
   end
 
+  create_table :organizations, :force => true do |t|
+    t.string :name
+  end
+
   create_table :owners, :primary_key => :owner_id ,:force => true do |t|
     t.string :name
   end