ruby - undefined method `model_name' with simple_form on Rails 5 -

i'm getting undefined method 'model_name' error simple_form when want edit basic post on rails 5.

show.html.haml:

= link_to "edit", edit_post_path(@post)

edit.html.haml:

= simple_form_for @post |f|     = f.input :title     = f.input :link     = f.input :description      = f.button :submit 

posts_controller.rb:

def show   @post = post.find(params[:id]) end  def edit end  def update   if @post.update(post_params)     redirect_to @post   else     render 'edit'   end end 

any idea?

def edit   @post = post.find(params[:id]) # <========= end