2 files changed, 66 insertions, 2 deletions
diff --git a/activemodel/lib/active_model/validations.rb b/activemodel/lib/active_model/validations.rb
index 36d89c2492..5779ba3b29 100644
--- a/activemodel/lib/active_model/validations.rb
+++ b/activemodel/lib/active_model/validations.rb
@@ -3,6 +3,7 @@ require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/hash/keys'
 require 'active_model/errors'
+require 'active_model/validations/callbacks'
 
 module ActiveModel
 
@@ -164,8 +165,7 @@ module ActiveModel
     def valid?(context = nil)
       current_context, self.validation_context = validation_context, context
       errors.clear
-      _run_validate_callbacks
-      errors.empty?
+      run_validations!
     ensure
       self.validation_context = current_context
     end
@@ -194,6 +194,13 @@ module ActiveModel
     #   end
     #
     alias :read_attribute_for_validation :send
+
+  protected
+  
+    def run_validations!
+      _run_validate_callbacks
+      errors.empty?
+    end
   end
 end
 
diff --git a/activemodel/lib/active_model/validations/callbacks.rb b/activemodel/lib/active_model/validations/callbacks.rb
new file mode 100644
index 0000000000..afd65d3dd5
--- /dev/null
+++ b/activemodel/lib/active_model/validations/callbacks.rb
@@ -0,0 +1,57 @@
+require 'active_support/callbacks'
+
+module ActiveModel
+  module Validations
+    module Callbacks
+      # == Active Model Validation callbacks
+      #
+      # Provides an interface for any class to have <tt>before_validation</tt> and
+      # <tt>after_validation</tt> callbacks.
+      #
+      # First, extend ActiveModel::Callbacks from the class you are creating:
+      #
+      #   class MyModel
+      #     include ActiveModel::Validations::Callbacks
+      #
+      #     before_validation :do_stuff_before_validation
+      #     after_validation  :do_tuff_after_validation
+      #   end
+      #
+      #   Like other before_* callbacks if <tt>before_validation</tt> returns false
+      #   then <tt>valid?</tt> will not be called.
+      extend ActiveSupport::Concern
+
+      included do
+        include ActiveSupport::Callbacks
+        define_callbacks :validation, :terminator => "result == false", :scope => [:kind, :name]
+      end
+
+      module ClassMethods
+        def before_validation(*args, &block)
+          options = args.last
+          if options.is_a?(Hash) && options[:on]
+            options[:if] = Array.wrap(options[:if])
+            options[:if] << "self.validation_context == :#{options[:on]}"
+          end
+          set_callback(:validation, :before, *args, &block)
+        end
+
+        def after_validation(*args, &block)
+          options = args.extract_options!
+          options[:prepend] = true
+          options[:if] = Array.wrap(options[:if])
+          options[:if] << "!halted && value != false"
+          options[:if] << "self.validation_context == :#{options[:on]}" if options[:on]
+          set_callback(:validation, :after, *(args << options), &block)
+        end
+      end
+
+    protected
+
+      # Overwrite run validations to include callbacks.
+      def run_validations!
+        _run_validation_callbacks { super }
+      end
+    end
+  end
+end