Clean up the implementation of AR::Dirty

This moves a bit more of the logic required for dirty checking into the
attribute objects. I had hoped to remove the `with_value_from_database`
stuff, but unfortunately just calling `dup` on the attribute objects
isn't enough, since the values might contain deeply nested data
structures. I think this can be cleaned up further.

This makes most dirty checking become lazy, and reduces the number of
object allocations and amount of CPU time when assigning a value. This
opens the door (but doesn't quite finish) to improving the performance
of writes to a place comparable to 4.1

1 files changed, 7 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index a79bf0366b..10b5fcab24 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -118,7 +118,7 @@ module ActiveRecord
         elsif mapping.has_value?(value)
           mapping.key(value)
         else
-          raise ArgumentError, "'#{value}' is not a valid #{name}"
+          assert_valid_value(value)
         end
       end
 
@@ -131,6 +131,12 @@ module ActiveRecord
         mapping.fetch(value, value)
       end
 
+      def assert_valid_value(value)
+        unless value.blank? || mapping.has_key?(value) || mapping.has_value?(value)
+          raise ArgumentError, "'#{value}' is not a valid #{name}"
+        end
+      end
+
       protected
 
       attr_reader :name, :mapping