1 files changed, 38 insertions, 16 deletions

diff --git a/activemodel/lib/active_model/conversion.rb b/activemodel/lib/active_model/conversion.rb
index 80a3ba51c3..48c53f0789 100644
--- a/activemodel/lib/active_model/conversion.rb
+++ b/activemodel/lib/active_model/conversion.rb
@@ -1,4 +1,3 @@
-require 'active_support/concern'
 require 'active_support/inflector'
 
 module ActiveModel
@@ -18,17 +17,23 @@ module ActiveModel
   #   end
   #
   #   cm = ContactMessage.new
-  #   cm.to_model == self # => true
-  #   cm.to_key           # => nil
-  #   cm.to_param         # => nil
-  #   cm.to_path          # => "contact_messages/contact_message"
-  #
+  #   cm.to_model == cm  # => true
+  #   cm.to_key          # => nil
+  #   cm.to_param        # => nil
+  #   cm.to_partial_path # => "contact_messages/contact_message"
   module Conversion
     extend ActiveSupport::Concern
 
     # If your object is already designed to implement all of the Active Model
     # you can use the default <tt>:to_model</tt> implementation, which simply
-    # returns self.
+    # returns +self+.
+    #
+    #   class Person
+    #     include ActiveModel::Conversion
+    #   end
+    #
+    #   person = Person.new
+    #   person.to_model == person # => true
     #
     # If your model does not act like an Active Model object, then you should
     # define <tt>:to_model</tt> yourself returning a proxy object that wraps
@@ -37,29 +42,46 @@ module ActiveModel
       self
     end
 
-    # Returns an Enumerable of all key attributes if any is set, regardless
-    # if the object is persisted or not.
+    # Returns an Enumerable of all key attributes if any is set, regardless if
+    # the object is persisted or not. If there no key attributes, returns +nil+.
+    #
+    #   class Person < ActiveRecord::Base
+    #   end
     #
-    # Note the default implementation uses persisted? just because all objects
-    # in Ruby 1.8.x responds to <tt>:id</tt>.
+    #   person = Person.create
+    #   person.to_key # => [1]
     def to_key
-      persisted? ? [id] : nil
+      key = respond_to?(:id) && id
+      key ? [key] : nil
     end
 
-    # Returns a string representing the object's key suitable for use in URLs,
-    # or nil if <tt>persisted?</tt> is false.
+    # Returns a +string+ representing the object's key suitable for use in URLs,
+    # or +nil+ if <tt>persisted?</tt> is +false+.
+    #
+    #   class Person < ActiveRecord::Base
+    #   end
+    #
+    #   person = Person.create
+    #   person.to_param # => "1"
     def to_param
       persisted? ? to_key.join('-') : nil
     end
 
-    # Returns a string identifying the path associated with the object.
+    # Returns a +string+ identifying the path associated with the object.
     # ActionPack uses this to find a suitable partial to represent the object.
+    #
+    #   class Person
+    #     include ActiveModel::Conversion
+    #   end
+    #
+    #   person = Person.new
+    #   person.to_partial_path # => "people/person"
     def to_partial_path
       self.class._to_partial_path
     end
 
     module ClassMethods #:nodoc:
-      # Provide a class level cache for the to_path. This is an
+      # Provide a class level cache for #to_partial_path. This is an
       # internal method and should not be accessed directly.
       def _to_partial_path #:nodoc:
         @_to_partial_path ||= begin