I try to create a nested model form for the has_one association. (i\'m using Rails 4)
In my user, and adress model i have the following :
class User
in your controller UsersController, in the update method, add the address: :id to the address permitted attributes. Like this:
UsersController
update
address: :id
params.require(:user).permit(:user_name, address_attributes: [:id, :street]))