Ejemplo de un helper method en el controller, utilizado en el controller y en la vista

show.html.erb

<%- ... -%>

<h1>
  Detalles del docente <%= display_teacher(@teacher) -%>
</h1>

<%- ... -%>

teachers_controller.rb

class TeachersController < ApplicationController
  before_action :set_teacher, only: :show
  
  def index
    @teachers = Teacher.order(:surname, :name)
  end
  
  def show; end
  
  def new; end
  
  def create
    @teacher = Teacher.new(teacher_params)
    if @teacher.save
      redirect_to teachers_path, notice: "El docente #{display_teacher(@teacher)} ha sido creado correctamente."
    else
      render :new
    end
  end
  
  private
  
  def display_teacher(teacher)
    "#{teacher.surname}, #{teacher.name}"
  end
  helper_method :display_teacher
end