2 files changed, 23 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 365fdeb55a..ba64b8ee2f 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -39,6 +39,20 @@ module ActiveRecord
         end
         alias :primary_key= :set_primary_key
       end
+
+      module InstanceMethods
+
+        # Returns this record's primary key value wrapped in an Array
+        # or nil if the record is a new_record?
+        # This is done to comply with the AMo interface that expects
+        # every AMo compliant object to respond_to?(:key) and return
+        # an Enumerable object from that call, or nil if new_record?
+        def key
+          new_record? ? nil : [ self.id ]
+        end
+
+      end
+
     end
   end
 end
diff --git a/activerecord/test/cases/pk_test.rb b/activerecord/test/cases/pk_test.rb
index c121e0aa0f..2502c136cc 100644
--- a/activerecord/test/cases/pk_test.rb
+++ b/activerecord/test/cases/pk_test.rb
@@ -9,6 +9,15 @@ require 'models/mixed_case_monkey'
 class PrimaryKeysTest < ActiveRecord::TestCase
   fixtures :topics, :subscribers, :movies, :mixed_case_monkeys
 
+  def test_key
+    # test new record
+    topic = Topic.new
+    assert topic.key.nil?
+    # test existing record
+    topic = Topic.find(1)
+    assert_equal topic.key, [1]
+  end
+
   def test_integer_key
     topic = Topic.find(1)
     assert_equal(topics(:first).author_name, topic.author_name)