class Section < ActiveRecord::Base
belongs_to :course
has_many :quizzes, foreign_key: "lesson_id"
has_many :lessons, foreign_key: "section_id"#, :inverse_of => :sections
accepts_nested_attributes_for :lessons

rails_admin do
   create do
    field :course do
      default_value do
        Course.last.id
      end
     end
    field :title
  end

edit do
  field :course do
      default_value do
        Course.last.id
      end
  end
  field :title
end
end

 rails_admin do
   configure :lessons do
     field :title  # This is the line that is giving the error
     field :body
     field :image

    end
end

end

class Lesson < ActiveRecord::Base

 belongs_to :section #, foreign_key: "section_id"#, :inverse_of => :lessons
 has_many :posts, foreign_key: "lesson_id"
 has_one :quiz, :inverse_of => :lesson
 accepts_nested_attributes_for :quiz