Ensure correct record is returned when preloading has_one where more than one row exists

Signed-off-by: Michael Koziarski <michael@koziarski.com>
[#73 state:closed]

activerecord/lib/active_record/association_preload.rb

@@ -65,7 +65,13 @@ module ActiveRecord
       end
 
       def set_association_single_records(id_to_record_map, reflection_name, associated_records, key)
+        seen_keys = {}
         associated_records.each do |associated_record|
+          #this is a has_one or belongs_to: there should only be one record.
+          #Unfortunately we can't (in portable way) ask the database for 'all records where foo_id in (x,y,z), but please
+          # only one row per distinct foo_id' so this where we enforce that
+          next if seen_keys[associated_record[key].to_s]
+          seen_keys[associated_record[key].to_s] = true
           mapped_records = id_to_record_map[associated_record[key].to_s]
           mapped_records.each do |mapped_record|
             mapped_record.send("set_#{reflection_name}_target", associated_record)
@@ -122,7 +128,6 @@ module ActiveRecord
         else
           records.each {|record| record.send("set_#{reflection.name}_target", nil)}
 
-
           set_association_single_records(id_to_record_map, reflection.name, find_associated_records(ids, reflection, preload_options), reflection.primary_key_name)
         end
       end

activerecord/test/cases/associations/eager_test.rb

@@ -29,6 +29,10 @@ class EagerAssociationTest < ActiveRecord::TestCase
     post = Post.find(:first, :include => :comments, :conditions => "posts.title = 'Welcome to the weblog'")
     assert_equal 2, post.comments.size
     assert post.comments.include?(comments(:greetings))
+
+    posts = Post.find(:all, :include => :last_comment)
+    post = posts.find { |p| p.id == 1 }
+    assert_equal Post.find(1).last_comment, post.last_comment
   end
 
   def test_loading_conditions_with_or

activerecord/test/models/post.rb

@@ -9,6 +9,8 @@ class Post < ActiveRecord::Base
 
   belongs_to :author_with_posts, :class_name => "Author", :foreign_key => :author_id, :include => :posts
 
+  has_one :last_comment, :class_name => 'Comment', :order => 'id desc'
+
   has_many   :comments, :order => "body" do
     def find_most_recent
       find(:first, :order => "id DESC")