Make Model.exists? use relation.exists?

activerecord/lib/active_record/base.rb

@@ -732,10 +732,13 @@ def find_by_sql(sql)
       #   Person.exists?(:name => "David")
       #   Person.exists?(['name LIKE ?', "%#{query}%"])
       #   Person.exists?
-      def exists?(id_or_conditions = {})
-        find_initial(
-          :select => "#{quoted_table_name}.#{primary_key}",
-          :conditions => expand_id_conditions(id_or_conditions)) ? true : false
+      def exists?(id_or_conditions = nil)
+        case id_or_conditions
+        when Array, Hash
+          where(id_or_conditions).exists?
+        else
+          scoped.exists?(id_or_conditions)
+        end
       end
 
       # Creates an object (or multiple objects) and saves it to the database, if validations pass.
@@ -1874,14 +1877,6 @@ def attribute_condition(quoted_column_name, argument)
           end
         end
 
-        # Interpret Array and Hash as conditions and anything else as an id.
-        def expand_id_conditions(id_or_conditions)
-          case id_or_conditions
-            when Array, Hash then id_or_conditions
-            else sanitize_sql(primary_key => id_or_conditions)
-          end
-        end
-
       protected
         # Scope parameters to method calls within the block.  Takes a hash of method_name => parameters hash.
         # method_name may be <tt>:find</tt> or <tt>:create</tt>. <tt>:find</tt> parameters may include the <tt>:conditions</tt>, <tt>:joins</tt>,