correct ordering algorithm

lib/concern/positionable.rb

@@ -9,6 +9,12 @@ module Concern
     end
 
     def move_to(position)
+
+      self.exec_sql "
+      UPDATE #{self.class.table_name}
+      SET position = position - 1
+      WHERE position > :position AND position > 0", {position: self.position}
+
       self.exec_sql "
       UPDATE #{self.class.table_name}
       SET position = :position

spec/components/concern/positionable_spec.rb

@@ -34,11 +34,13 @@ describe Concern::Positionable do
       positions.should == [3,0,1,2,4]
       TestItem.pluck(:position).sort.should == [0,1,2,3,4]
 
+      TestItem.find(3).move_to(1)
+      positions.should == [0,3,1,2,4]
 
       # this is somewhat odd, but when there is not positioning
       # not much we can do
       TestItem.find(1).move_to(5)
-      positions.should == [3,0,2,4,1]
+      positions.should == [0,3,2,4,1]
 
       TestItem.pluck(:position).sort.should == [0,1,2,3,4]