вложенная форма имеет много сквозных рельсов4

Я не получаю ожидаемых результатов, Навыки не сохраняются. Я хочу, чтобы у каждого человека был ТОЛЬКО 1 основной навык.

DB

  # Table name: people
  #
  #  id          :integer          not null, primary key
  #  first_name  :string(255)
  #  last_name   :string(255)
  #  headline    :string(255)
  #  description :string(255)
  #  user_id     :integer
  #  created_at  :datetime
  #  updated_at  :datetime
  #

  # == Schema Information
  #
  # Table name: skills
  #
  #  id          :integer          not null, primary key
  #  title       :string(255)
  #  description :text
  #  created_at  :datetime
  #  updated_at  :datetime
  #

  # == Schema Information
  #
  # Table name: entity_skills
  #
  #  id          :integer          not null, primary key
  #  skill_id    :integer
  #  person_id   :integer
  #  created_at  :datetime
  #  updated_at  :datetime
  #

Модели

class Person < ActiveRecord::Base
  has_many :entity_skills
  has_many :skills, through: :entity_skills, foreign_key: "person_id"
  accepts_nested_attributes_for :skills
end


class Skill < ActiveRecord::Base
 has_many :entity_skills
 has_many :people, through: :entity_skills, foreign_key: "person_id"
end

class EntitySkill < ActiveRecord::Base
  belongs_to :person
  belongs_to :skill
end

Контроллер

def new
  @person = Person.new
  @all_skills = Skill.all
  @entity_skills = @person.skills.build

end

def edit
  @all_skills = Skill.all

  @entity_skills = @person.entity_skills.build
end

def create
  @person = Person.new(person_params)

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

 def person_params
  params.require(:person).permit(:first_name, :last_name, :headline, :description, :user_id, :employer_id, skills_attributes: [:id])
end

Форма

<%= form_for(@person) do |f| %>
  ....
  ....
  <h2>Skills</h2>
    <%= f.fields_for @entity_skills do |es| %>
        <%= es.label "All Skills" %>
        <%= collection_select(:skills, :id, @all_skills, :id, :title) %>
    <% end %>

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

На скиллы ничего не сохраняется, может кто-нибудь объяснить в чем дело?