to_key should return all exists keys (if any exists), regardless if the object is persisted or not. If you need it to reflect persistance, you should use to_param.

2 files changed, 7 insertions, 3 deletions

diff --git a/activemodel/lib/active_model/conversion.rb b/activemodel/lib/active_model/conversion.rb
index b998a59e81..ae0ab93e97 100644
--- a/activemodel/lib/active_model/conversion.rb
+++ b/activemodel/lib/active_model/conversion.rb
@@ -33,8 +33,11 @@ module ActiveModel
       self
     end
 
-    # Returns an Enumerable of all (primary) key attributes or nil if
-    # persisted? is false
+    # Returns an Enumerable of all key attributes if any is set, regardless
+    # if the object is persisted or not.
+    #
+    # Note the default implementation uses persisted? just because all objects
+    # in Ruby 1.8.x responds to :id.
     def to_key
       persisted? ? [id] : nil
     end
@@ -42,7 +45,7 @@ module ActiveModel
     # Returns a string representing the object's key suitable for use in URLs,
     # or nil if persisted? is false
     def to_param
-      to_key ? to_key.join('-') : nil
+      persisted? ? to_key.join('-') : nil
     end
   end
 end
diff --git a/activemodel/lib/active_model/lint.rb b/activemodel/lib/active_model/lint.rb
index 26eb4a3c41..d7a6da48ca 100644
--- a/activemodel/lib/active_model/lint.rb
+++ b/activemodel/lib/active_model/lint.rb
@@ -38,6 +38,7 @@ module ActiveModel
       # not persisted?, then to_param should always return nil.
       def test_to_param
         assert model.respond_to?(:to_param), "The model should respond to to_param"
+        def model.to_key() [1] end
         def model.persisted?() false end
         assert model.to_param.nil?
       end