has_many :classroom_students
has_many :students, through: :classroom_students

has_many :classroom_students
has_many :classrooms, through: :classroom_students

def import
        @students = Student.all
        if params[:file].present?
        Student.import(params[:file], current_user.id)
        redirect_to students_path, notice: 'Students imported.'
      else
        redirect_to students_path, notice: "You need to choose a file first!"
        end
      end