2 files changed, 75 insertions, 1 deletions
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index b17f72741a..dc0bd2d125 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -1,10 +1,13 @@
 module ActiveRecord
   module AttributeMethods #:nodoc:
     DEFAULT_SUFFIXES = %w(= ? _before_type_cast)
+    ATTRIBUTE_TYPES_CACHED_BY_DEFAULT = [:datetime, :timestamp, :time, :date]
 
     def self.included(base)
       base.extend ClassMethods
       base.attribute_method_suffix *DEFAULT_SUFFIXES
+      base.cattr_accessor :attribute_types_cached_by_default, :instance_writer => false
+      base.attribute_types_cached_by_default = ATTRIBUTE_TYPES_CACHED_BY_DEFAULT
     end
 
     # Declare and check for suffixed attribute methods.
@@ -88,6 +91,23 @@ module ActiveRecord
       
       alias :define_read_methods :define_attribute_methods
 
+      # +cache_attributes+ allows you to declare which converted attribute values should
+      # be cached. Usually caching only pays off for attributes with expensive conversion
+      # methods, like date columns (e.g. created_at, updated_at).
+      def cache_attributes(*attribute_names)
+        attribute_names.each {|attr| cached_attributes << attr.to_s}
+      end
+
+      # returns the attributes where
+      def cached_attributes
+        @cached_attributes ||=
+          columns.select{|c| attribute_types_cached_by_default.include?(c.type)}.map(&:name).to_set
+      end
+
+      def cache_attribute?(attr_name)
+        cached_attributes.include?(attr_name)
+      end
+
       private
         # Suffixes a, ?, c become regexp /(a|\?|c)$/
         def rebuild_attribute_method_regexp
@@ -109,7 +129,10 @@ module ActiveRecord
             access_code = access_code.insert(0, "missing_attribute('#{attr_name}', caller) unless @attributes.has_key?('#{attr_name}'); ")
           end
           
-          evaluate_attribute_method attr_name, "def #{symbol}; @attributes_cache['#{attr_name}'] ||= begin; #{access_code}; end; end"
+          if cache_attribute?(attr_name)
+            access_code = "@attributes_cache['#{attr_name}'] ||= (#{access_code})"
+          end
+          evaluate_attribute_method attr_name, "def #{symbol}; #{access_code}; end"
         end
 
         # Define read method for serialized attribute.
diff --git a/activerecord/test/attribute_methods_test.rb b/activerecord/test/attribute_methods_test.rb
index f16b264c35..8646afdcb5 100755
--- a/activerecord/test/attribute_methods_test.rb
+++ b/activerecord/test/attribute_methods_test.rb
@@ -2,6 +2,7 @@ require 'abstract_unit'
 require 'fixtures/topic'
 
 class AttributeMethodsTest < Test::Unit::TestCase
+  fixtures :topics
   def setup
     @old_suffixes = ActiveRecord::Base.send(:attribute_method_suffixes).dup
     @target = Class.new(ActiveRecord::Base)
@@ -92,4 +93,54 @@ class AttributeMethodsTest < Test::Unit::TestCase
       end
     end
   end
+
+  def test_only_time_related_columns_are_meant_to_be_cached_by_default
+    expected = %w(datetime timestamp time date).sort
+    assert_equal expected, ActiveRecord::Base.attribute_types_cached_by_default.map(&:to_s).sort
+end
+
+  def test_declaring_attributes_as_cached_adds_them_to_the_attributes_cached_by_default
+    default_attributes = Topic.cached_attributes
+    Topic.cache_attributes :replies_count
+    expected = default_attributes + ["replies_count"]
+    assert_equal expected.sort, Topic.cached_attributes.sort
+    Topic.instance_variable_set "@cached_attributes", nil
+  end
+
+  def test_time_related_columns_are_actually_cached
+    column_types = %w(datetime timestamp time date).map(&:to_sym)
+    column_names = Topic.columns.select{|c| column_types.include?(c.type) }.map(&:name)
+
+    assert_equal column_names.sort, Topic.cached_attributes.sort
+    assert_equal time_related_columns_on_topic.sort, Topic.cached_attributes.sort
+  end
+
+  def test_accessing_cached_attributes_caches_the_converted_values_and_nothing_else
+    t = topics(:first)
+    cache = t.instance_variable_get "@attributes_cache"
+
+    assert_not_nil cache
+    assert cache.empty?
+
+    all_columns = Topic.columns.map(&:name)
+    cached_columns = time_related_columns_on_topic
+    uncached_columns =  all_columns - cached_columns
+
+    all_columns.each do |attr_name|
+      attribute_gets_cached = Topic.cache_attribute?(attr_name)
+      val = t.send attr_name unless attr_name == "type"
+      if attribute_gets_cached
+        assert cached_columns.include?(attr_name)
+        assert_equal val, cache[attr_name]
+      else
+        assert uncached_columns.include?(attr_name)
+        assert !cache.include?(attr_name)
+      end
+    end
+  end
+
+  private
+  def time_related_columns_on_topic
+    Topic.columns.select{|c| [:time, :date, :datetime, :timestamp].include?(c.type)}.map(&:name)
+  end
 end