illnesses_controller.rb

class IllnessesController < ApplicationController
  before_action :set_illness, only: [:show, :edit, :update, :destroy]

  # GET /illnesses
  def index
    @illnesses = Illness.all
  end

  # GET /illness/1
  def show
  end

  # GET /illness/new
  def new
    @illness = Illness.new
  end

  # GET /illness/1/edit
  def edit
  end

  # POST /illness
  def create
    @illness = Illness.new(illness_params)

    respond_to do |format|
      if @illness.save
        format.html { redirect_to @illness, notice: 'Illness was successfully created.' }
        format.json { render :show, status: :created, location: @illness }
      else
        format.html { render :new }
        format.json { render json: @illness.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /illness/1
  def update
    respond_to do |format|
      if @illness.update(illness_params)
        format.html { redirect_to @illness, notice: 'Illness was successfully updated.' }
        format.json { render :show, status: :ok, location: @illness }
      else
        format.html { render :edit }
        format.json { render json: @illness.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /illness/1
  def destroy
    @illness.destroy
    respond_to do |format|
      format.html { redirect_to illnesses_url, notice: 'Illness was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_illness
      @illness = Illness.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def illness_params
      params.require(:illness).permit(:name, :etiology, :patogenesis, :incidence, :prevalence, :category, :anamnesis,
                                    clinical_attributes: [:id, :inspection, :_destroy])
    end
end

view.html.erb

<%= simple_form_for(illness) do |f| %>
  <% if illness.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(illness.errors.count, "error") %> prohibited this illness from being saved:</h2>

      <ul>
      <% illness.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

    <%= f.input :name %>
    <%= f.input :etiology %>
    <%= f.input :patogenesis %>
    <%= f.input :incidence %>
    <%= f.input :prevalence %>
    <%= f.input :category %>
    <%= f.simple_fields_for :clinical do |clinic| %>
      <%= clinic.input :inspection %>
    <% end %>


  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>