4 files changed, 28 insertions, 14 deletions
diff --git a/activemodel/lib/active_model/errors.rb b/activemodel/lib/active_model/errors.rb
index f90030641d..8337b04c0d 100644
--- a/activemodel/lib/active_model/errors.rb
+++ b/activemodel/lib/active_model/errors.rb
@@ -205,21 +205,14 @@ module ActiveModel
       messages.dup
     end
 
-    # Adds +message+ to the error messages on +attribute+, which will be returned on a call to
-    # <tt>on(attribute)</tt> for the same attribute. More than one error can be added to the same
-    # +attribute+ in which case an array will be returned on a call to <tt>on(attribute)</tt>.
+    # Adds +message+ to the error messages on +attribute+. More than one error can be added to the same
+    # +attribute+.
     # If no +message+ is supplied, <tt>:invalid</tt> is assumed.
     #
     # If +message+ is a symbol, it will be translated using the appropriate scope (see +translate_error+).
     # If +message+ is a proc, it will be called, allowing for things like <tt>Time.now</tt> to be used within an error.
     def add(attribute, message = nil, options = {})
-      message ||= :invalid
-
-      if message.is_a?(Symbol)
-        message = generate_message(attribute, message, options.except(*CALLBACKS_OPTIONS))
-      elsif message.is_a?(Proc)
-        message = message.call
-      end
+      message = normalize_message(attribute, message, options)
       if options[:strict]
         raise ActiveModel::StrictValidationFailed,  message
       end
@@ -244,6 +237,15 @@ module ActiveModel
       end
     end
 
+    # Returns true if an error on the attribute with the given message is present, false otherwise.
+    # +message+ is treated the same as for +add+.
+    #   p.errors.add :name, :blank
+    #   p.errors.added? :name, :blank # => true
+    def added?(attribute, message = nil, options = {})
+      message = normalize_message(attribute, message, options)
+      self[attribute].include? message
+    end
+
     # Returns all the full error messages in an array.
     #
     #   class Company
@@ -329,6 +331,19 @@ module ActiveModel
 
       I18n.translate(key, options)
     end
+
+  private
+    def normalize_message(attribute, message, options)
+      message ||= :invalid
+
+      if message.is_a?(Symbol)
+        generate_message(attribute, message, options.except(*CALLBACKS_OPTIONS))
+      elsif message.is_a?(Proc)
+        message.call
+      else
+        message
+      end
+    end
   end
 
   class StrictValidationFailed < StandardError
diff --git a/activemodel/lib/active_model/observing.rb b/activemodel/lib/active_model/observing.rb
index 7a910d18e7..cd8eb357de 100644
--- a/activemodel/lib/active_model/observing.rb
+++ b/activemodel/lib/active_model/observing.rb
@@ -187,8 +187,7 @@ module ActiveModel
       def observe(*models)
         models.flatten!
         models.collect! { |model| model.respond_to?(:to_sym) ? model.to_s.camelize.constantize : model }
-        remove_possible_method(:observed_classes)
-        define_method(:observed_classes) { models }
+        redefine_method(:observed_classes) { models }
       end
 
       # Returns an array of Classes to observe.
diff --git a/activemodel/lib/active_model/validations/validates.rb b/activemodel/lib/active_model/validations/validates.rb
index fbceb81e8f..8e09f6ac35 100644
--- a/activemodel/lib/active_model/validations/validates.rb
+++ b/activemodel/lib/active_model/validations/validates.rb
@@ -57,7 +57,7 @@ module ActiveModel
       #
       # Additionally validator classes may be in another namespace and still used within any class.
       #
-      #   validates :name, :'file/title' => true
+      #   validates :name, :'film/title' => true
       #
       # The validators hash can also handle regular expressions, ranges, 
       # arrays and strings in shortcut form, e.g.
diff --git a/activemodel/lib/active_model/validator.rb b/activemodel/lib/active_model/validator.rb
index 0e444738ba..35ec98c822 100644
--- a/activemodel/lib/active_model/validator.rb
+++ b/activemodel/lib/active_model/validator.rb
@@ -57,7 +57,7 @@ module ActiveModel #:nodoc:
   # To add behavior to the initialize method, use the following signature:
   #
   #   class MyValidator < ActiveModel::Validator
-  #     def initialize(record, options)
+  #     def initialize(options)
   #       super
   #       @my_custom_field = options[:field_name] || :first_name
   #     end