Rails 3 app model how ensure only one boolean field set to true at a time

Question

I have a Logo model that has fields of name:string, default:boolean. I want the true value to be unique, so that only one item in the database can be set to true at once. How do

Answer 1

if you want this to work for creating and updating (rails v4) make note of this tidbit from rails guides

after_save runs both on create and update, but always after the more specific callbacks after_create and after_update, no matter the order in which the macro calls were executed.