Rails 4 simple_form has_many 通过复选框不保存

我正在尝试使用 simple_form 通过复选框来实现员工经常性扣除表。我的代码有效，但所选的经常性扣除未保存在我的表中。我不明白为什么。

这是我的模型。

class Employee < ActiveRecord::Base
  belongs_to :club
  has_many :employee_recurrents 
  has_many :recurrents, :through => :employee_recurrents
end

class Recurrent < ActiveRecord::Base
  belongs_to :club
  has_many :employee_recurrents 
  has_many :employees, :through => :employee_recurrents
end

class EmployeeRecurrent < ActiveRecord::Base
  belongs_to :employee
  belongs_to :recurrent 
end

移民

class CreateEmployeeRecurrents < ActiveRecord::Migration
  def change
    create_table :employee_recurrents, :id => false do |t|

      t.references :employee
      t.references :recurrent 

  end

  add_index :employee_recurrents, [:employee_id, :recurrent_id]
  add_index :employee_recurrents, [:recurrent_id, :employee_id]

 end
end

form

<%= simple_form_for @employee, html: {class: 'form-horizontal' } do |f| %>

  <%= f.error_notification %>

  <%= f.input :first_name %>
  <%= f.input :last_name %>

  <%= f.association :recurrents, 
                     as: :check_boxes, 
                     label_method: :description, 
                     value_method: :id,
                     label: 'Recurrent Deductions' %>

  <%= f.button :submit, class: 'btn btn-primary' %>
<% end %>

控制器

def employee_params
  params.require(:employee).permit(:first_name, :recurrent_ids)
end

这是我编辑的日志

Started PATCH "/employees/1" for 127.0.0.1 at 2013-08-12 19:38:42 +0800
Processing by EmployeesController#update as HTML
  Parameters: {"utf8"=>"✓",       "authenticity_token"=>"IwWzcT2qQJqHkTumWjb3OD5nJe9xLaA+YezMumer9X8=", "employee"=>{"job_id"=>"5", "manager_id"=>"", "first_name"=>"Mark", "recurrent_ids"=>["1", ""]}, "commit"=>"Update Employee", "id"=>"1"}
  [1m[36mActiveRecord::SessionStore::Session Load (1.2ms)[0m  [1mSELECT "sessions".* FROM "sessions" WHERE "sessions"."session_id" = '9a8b066a4033f8fa2ed867371ffaa2a3' ORDER BY "sessions"."id" ASC LIMIT 1[0m
  [1m[35mUser Load (0.5ms)[0m  SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
  [1m[36mEmployee Load (0.8ms)[0m  [1mSELECT "employees".* FROM "employees" WHERE "employees"."id" = $1 ORDER BY last_name, first_name LIMIT 1[0m  [["id", "1"]]
Unpermitted parameters: recurrent_ids
  [1m[35m (0.6ms)[0m  BEGIN
  [1m[36mEmployee Exists (1.1ms)[0m  [1mSELECT 1 AS one FROM "employees" WHERE ("employees"."email" = '[email protected] /cdn-cgi/l/email-protection' AND "employees"."id" != 1 AND "employees"."club_id" = 1) LIMIT 1[0m
  [1m[35m (0.4ms)[0m  COMMIT
Redirected to http://localhost:3000/employees
Completed 302 Found in 22ms (ActiveRecord: 4.6ms)

我需要以下强参数

def employee_params
  params.require(:employee).permit(:first_name, :recurrent_ids => [])
end