adding data from the model

Hi, I have a form that I need to add default data when is passed into the DB.. for example I have a create post, were the user can add tittle, text etc.. but I need to add who created so is on record etc I will like to know how will I do this from the model, since I think that is the right place to do this.. on php I will just add hiden fields to the form and pass the variables but there should be a nice way in rails..


Post.create( params[:post].merge( :user_id => session[:user_id] ) )