Add validators reflection so you can do 'Person.validators' and 'Person.validators_on(:name)'.

Signed-off-by: José Valim <jose.valim@gmail.com>

activemodel/lib/active_model/validations.rb

@@ -1,4 +1,5 @@
 require 'active_support/core_ext/array/extract_options'
+require 'active_support/core_ext/class/attribute'
 require 'active_support/core_ext/hash/keys'
 require 'active_model/errors'
 
@@ -45,6 +46,9 @@ module ActiveModel
     included do
       extend ActiveModel::Translation
       define_callbacks :validate, :scope => :name
+
+      class_attribute :_validators
+      self._validators = Hash.new { |h,k| h[k] = [] }
     end
 
     module ClassMethods
@@ -118,7 +122,18 @@ module ActiveModel
         set_callback(:validate, *args, &block)
       end
 
-      private
+      # List all validators that being used to validate the model using +validates_with+
+      # method.
+      def validators
+        _validators.values.flatten.uniq
+      end
+
+      # List all validators that being used to validate a specific attribute.
+      def validators_on(attribute)
+        _validators[attribute.to_sym]
+      end
+
+    private
 
       def _merge_attributes(attr_names)
         options = attr_names.extract_options!

activemodel/lib/active_model/validations/with.rb

@@ -62,6 +62,15 @@ module ActiveModel
         args.each do |klass|
           validator = klass.new(options, &block)
           validator.setup(self) if validator.respond_to?(:setup)
+
+          if validator.respond_to?(:attributes) && !validator.attributes.empty?
+            validator.attributes.each do |attribute|
+              _validators[attribute.to_sym] << validator
+            end
+          else
+            _validators[nil] << validator
+          end
+
           validate(validator, options)
         end
       end

activemodel/lib/active_model/validator.rb

@@ -1,3 +1,5 @@
+require "active_support/core_ext/module/anonymous"
+
 module ActiveModel #:nodoc:
   # A simple base class that can be used along with 
   # +ActiveModel::Validations::ClassMethods.validates_with+
@@ -88,11 +90,27 @@ module ActiveModel #:nodoc:
   class Validator
     attr_reader :options
 
+    # Returns the kind of the validator.
+    #
+    # == Examples
+    #
+    #   PresenceValidator.kind    #=> :presence
+    #   UniquenessValidator.kind  #=> :uniqueness
+    #
+    def self.kind
+      @kind ||= name.split('::').last.underscore.sub(/_validator$/, '').to_sym unless anonymous?
+    end
+
     # Accepts options that will be made availible through the +options+ reader.
     def initialize(options)
       @options = options
     end
 
+    # Return the kind for this validator.
+    def kind
+      self.class.kind
+    end
+
     # Override this method in subclasses with validation logic, adding errors
     # to the records +errors+ array where necessary.
     def validate(record)

activemodel/test/cases/validations/with_validation_test.rb

@@ -9,6 +9,7 @@ class ValidatesWithTest < ActiveRecord::TestCase
 
   def teardown
     Topic.reset_callbacks(:validate)
+    Topic._validators.clear
   end
 
   ERROR_MESSAGE = "Validation error from validator"

activemodel/test/cases/validations_test.rb

@@ -10,6 +10,10 @@ require 'models/custom_reader'
 class ValidationsTest < ActiveModel::TestCase
   include ActiveModel::TestsDatabase
 
+  def setup
+    Topic._validators.clear
+  end
+
   # Most of the tests mess with the validations of Topic, so lets repair it all the time.
   # Other classes we mess with will be dealt with in the specific tests
   def teardown
@@ -220,4 +224,27 @@ class ValidationsTest < ActiveModel::TestCase
     assert !t.valid?
     assert ["NO BLANKS HERE"], t.errors[:title]
   end
+
+  def test_list_of_validators_for_model
+    Topic.validates_presence_of :title
+    Topic.validates_length_of :title, :minimum => 2
+
+    assert_equal 2, Topic.validators.count
+    assert_equal [:presence, :length], Topic.validators.map(&:kind)
+  end
+
+  def test_list_of_validators_on_an_attribute
+    Topic.validates_presence_of :title, :content
+    Topic.validates_length_of :title, :minimum => 2
+
+    assert_equal 2, Topic.validators_on(:title).count
+    assert_equal [:presence, :length], Topic.validators_on(:title).map(&:kind)
+    assert_equal 1, Topic.validators_on(:content).count
+    assert_equal [:presence], Topic.validators_on(:content).map(&:kind)
+  end
+
+  def test_accessing_instance_of_validator_on_an_attribute
+    Topic.validates_length_of :title, :minimum => 10
+    assert_equal 10, Topic.validators_on(:title).first.options[:minimum]
+  end
 end