try this gem
http://github.com/sam/dm-more/tree/master/dm-adjust

YourModel.all(:id => 1).adjust!(:counter => 1)

On 11월13일, 오후4시32분, __andrew <[EMAIL PROTECTED]> wrote:
> Hey All,
>
> I've recently switched from using ActiveRecord to DataMapper and the
> minor differences have made it a smooth transition so far. However, I
> can't seem to find any documentation on maintaining a counter. I have
> an integer column in my model that needs to be incremented
> periodically. My first inclination was to use model.update_attributes
> (), but this seems to be a bad idea because the database value could
> be overwritten before DataMapper can write. The SQL query:
>
> UPDATE table_name SET counter = counter + 1 WHERE id = n;
>
> accomplishes what I want to do. I've perused the DataMapper code and
> docs, but I can't seem to find a method that will abstract this.
> ActiveRecord's is called 'increment_counter'. Am I missing the simple
> way to do this?
>
> Andrew S.
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