ActiveModel::Validations::Callbacks should not be required by default.

activemodel/lib/active_model/validations.rb

@@ -46,7 +46,6 @@ module ActiveModel
   module Validations
     extend ActiveSupport::Concern
     include ActiveSupport::Callbacks
-    include ActiveModel::Validations::Callbacks
 
     included do
       extend ActiveModel::Translation
@@ -160,6 +159,17 @@ module ActiveModel
       @errors ||= Errors.new(self)
     end
 
+    # Runs all the specified validations and returns true if no errors were added
+    # otherwise false. Context can optionally be supplied to define which callbacks
+    # to test against (the context is defined on the validations using :on).
+    def valid?(context = nil)
+      current_context, self.validation_context = validation_context, context
+      errors.clear
+      run_validations!
+    ensure
+      self.validation_context = current_context
+    end
+
     # Performs the opposite of <tt>valid?</tt>. Returns true if errors were added, 
     # false otherwise.
     def invalid?(context = nil)
@@ -184,6 +194,13 @@ module ActiveModel
     #   end
     #
     alias :read_attribute_for_validation :send
+
+  protected
+  
+    def run_validations!
+      _run_validate_callbacks
+      errors.empty?
+    end
   end
 end
 

activemodel/lib/active_model/validations/callbacks.rb

@@ -46,19 +46,12 @@ module ActiveModel
         end
       end
 
-      # Runs all the specified validations and returns true if no errors were added
-      # otherwise false. Context can optionally be supplied to define which callbacks
-      # to test against (the context is defined on the validations using :on).
-      def valid?(context = nil)
-        current_context, self.validation_context = validation_context, context
-        errors.clear
-        @validate_callback_result = nil
-        validation_callback_result = _run_validation_callbacks { @validate_callback_result = _run_validate_callbacks }
-        (validation_callback_result && @validate_callback_result) ? errors.empty? : false
-      ensure
-        self.validation_context = current_context
-      end
+    protected
 
+      # Overwrite run validations to include callbacks.
+      def run_validations!
+        _run_validation_callbacks { super }
+      end
     end
   end
 end

activemodel/test/cases/validations/callbacks_test.rb

@@ -3,6 +3,7 @@ require 'cases/helper'
 
 class Dog
   include ActiveModel::Validations
+  include ActiveModel::Validations::Callbacks
 
   attr_accessor :name, :history
 

activerecord/lib/active_record/base.rb

@@ -1874,7 +1874,6 @@ module ActiveRecord #:nodoc:
     extend ActiveSupport::DescendantsTracker
 
     include ActiveModel::Conversion
-    include ActiveModel::Validations::Callbacks
     include Validations
     extend CounterCache
     include Locking::Optimistic, Locking::Pessimistic

activerecord/lib/active_record/callbacks.rb

@@ -234,8 +234,7 @@ module ActiveRecord
 
     included do
       extend ActiveModel::Callbacks
-
-      attr_accessor :validation_context
+      include ActiveModel::Validations::Callbacks
 
       define_model_callbacks :initialize, :find, :only => :after
       define_model_callbacks :save, :create, :update, :destroy
@@ -249,12 +248,6 @@ module ActiveRecord
           send(meth.to_sym, meth.to_sym)
         end
       end
-
-    end
-
-    def valid?(*) #:nodoc:
-      self.validation_context = new_record? ? :create : :update
-      super 
     end
 
     def destroy #:nodoc:
@@ -269,6 +262,7 @@ module ActiveRecord
     end
 
   private
+
     def create_or_update #:nodoc:
       _run_save_callbacks { super }
     end