Further refactor the schema implementation

lib/paperclip/schema.rb

@@ -12,21 +12,26 @@ module Paperclip
                  :updated_at   => :datetime}
 
     def has_attached_file(attachment_name)
-      @@columns.each do |name, type|
-        column_name = full_column_name(attachment_name, name)
-        column(column_name, type)
+      with_columns_for(attachment_name) do |column_name, column_type|
+        column(column_name, column_type)
       end
     end
 
     def drop_attached_file(table_name, attachment_name)
-      @@columns.each do |name, type|
-        column_name = full_column_name(attachment_name, name)
+      with_columns_for(attachment_name) do |column_name, column_type|
         remove_column(table_name, column_name)
       end
     end
 
     protected
 
+    def with_columns_for(attachment_name)
+      @@columns.each do |suffix, column_type|
+        column_name = full_column_name(attachment_name, suffix)
+        yield column_name, column_type
+      end
+    end
+
     def full_column_name(attachment_name, column_name)
       "#{attachment_name}_#{column_name}".to_sym
     end