Ruby on Rails

I'm stuck and i don't know why it is not working right. I have a model  lesson wich has many sublessons. When i update the lesson rails update  properly the lesson attributes but is creating another sublessons  records instead of just updating it.    Here is my code    View Form:  <div style="padding:13px">  <%= form_for @lesson do |f| %>            <%= f.label :lesson_name, "Lesson title" %></br>            <%= f.text_field :lesson_name,  class: "form-control" %></br>            <%= f.label :lesson_icon, "Choise icon" %>            <%= f.select "lesson_icon", options_for_select([ "ico03",  "ico04","ico05","ico06" ])%></br></br>            <div>             <%= f.fields_for :sublessons do |sublesson_a| %>               <%= sublesson_a.label :sublesson_name, "Subtitle 1" %></br>             <%= sublesson_a.text_field :sublesson_name, class:  "form-control" %></br>             <%= sublesson_a.label :sublesson_content, "Content" %></br>             <%=sublesson_a.text_area 'sublesson_content', rows: 3, class:  'form-control'%></br>             <%= sublesson_a.label :sublesson_video_link, "Video link"  %><br>             <%= sublesson_a.text_field :sublesson_video_link, class:  "form-control" %></br>            <%end%>           </div>         </div>  <%= f.submit "Submit", class: "btn btn-primary" %>      <% end %>    </div>    lesson model  class Lesson < ActiveRecord::Base     has_many :sublessons, :dependent => :destroy     accepts_nested_attributes_for :sublessons, :reject_if => :all_blank  end  sublesson model    class Sublesson < ActiveRecord::Base    belongs_to :lesson, :foreign_key => "lesson_id"    validates :sublesson_name, presence: true    validates :sublesson_content ,presence: true  end    lesson controller    def update     @lesson = Lesson.find(params[:id])     @sublessons=@lesson.sublessons.all      if @lesson.update(lesson_params)        flash[:notice] = "Lesson updated"        redirect_to lessons_show_url      else        flash[:notice] = "Error"        redirect_to lessons_show_url      end  end    def edit      @lesson = Lesson.find(params[:id])      @sublessons=@lesson.sublessons.all  end      def lesson_params  params.require(:lesson).permit(:lesson_name, :lesson_icon,  sublessons_attributes:[:sublesson_id, :sublesson_name,  :sublesson_content, :sublesson_video_link])    end