Fix eagerly loading associations without primary keys

activerecord/lib/active_record/associations/join_dependency/join_part.rb

@@ -54,7 +54,7 @@ def column_names_with_alias
           unless @column_names_with_alias
             @column_names_with_alias = []
 
-            ([primary_key] + (column_names - [primary_key])).each_with_index do |column_name, i|
+            ([primary_key] + (column_names - [primary_key])).compact.each_with_index do |column_name, i|
               @column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
             end
           end

activerecord/test/cases/associations/eager_test.rb

@@ -39,6 +39,19 @@ def test_eager_with_has_one_through_join_model_with_conditions_on_the_through
     assert_nil member.favourite_club
   end
 
+  def test_loading_with_one_association_without_primary_key
+    Comment.primary_key = nil
+    begin
+      assert_nothing_raised do
+        Post.includes(:comments).references(:comments).all
+      end
+    rescue
+      raise $!
+    ensure
+      Comment.primary_key = 'id'
+    end
+  end
+
   def test_loading_with_one_association
     posts = Post.find(:all, :include => :comments)
     post = posts.find { |p| p.id == 1 }