ruby on rails - Calling modals from before_filters -

i have asked similar, more concrete.

i'm making login using twitter bootstrap modals , want write before save or create filter users (i don't know better), working this:

def before_save   if devise_error_messages     //stay in modal , show errors or notice   else    //call modal congratulations text   end end 

how can call devise_error_messages method models or how should this?

then, how can call js filters?