Improve performance of AR object instantiation

We introduced a performance hit by adding an additional iteration
through a model's attributes on creation. We don't actually need the
values from `Result` to be a hash, we can separate the columns and
values and zip them up ourself during the iteration that we have to do.

1 files changed, 8 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index f58145ab05..4aad3217cb 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -165,15 +165,19 @@ module ActiveRecord
       # record instance. For single-table inheritance, we check the record
       # for a +type+ column and return the corresponding class.
       def discriminate_class_for_record(record)
-        if using_single_table_inheritance?(record)
-          find_sti_class(record[inheritance_column])
+        discriminate_class_for_value(record[inheritance_column])
+      end
+
+      def discriminate_class_for_value(value)
+        if using_single_table_inheritance?(value)
+          find_sti_class(value)
         else
           super
         end
       end
 
-      def using_single_table_inheritance?(record)
-        record[inheritance_column].present? && columns_hash.include?(inheritance_column)
+      def using_single_table_inheritance?(value)
+        value.present? && columns_hash.include?(inheritance_column)
       end
 
       def find_sti_class(type_name)