title: Rails 4 simple_form has_many through check boxes not saving
body: <p>I am trying to implement an employee recurrent deductions table through check boxes using simple_form. My code works but the selected recurrent deductions are not saved in my table. I can't work out why.</p>
  
  <p>Here are my models.</p>
  
  <pre><code>class Employee &lt; ActiveRecord::Base
    belongs_to :club
    has_many :employee_recurrents 
    has_many :recurrents, :through =&gt; :employee_recurrents
  end
  
  class Recurrent &lt; ActiveRecord::Base
    belongs_to :club
    has_many :employee_recurrents 
    has_many :employees, :through =&gt; :employee_recurrents
  end
  
  class EmployeeRecurrent &lt; ActiveRecord::Base
    belongs_to :employee
    belongs_to :recurrent 
  end
  </code></pre>
  
  <p>migration</p>
  
  <pre><code>class CreateEmployeeRecurrents &lt; ActiveRecord::Migration
    def change
      create_table :employee_recurrents, :id =&gt; 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
  </code></pre>
  
  <p>form</p>
  
  <pre><code>&lt;%= simple_form_for @employee, html: {class: 'form-horizontal' } do |f| %&gt;
  
    &lt;%= f.error_notification %&gt;
  
    &lt;%= f.input :first_name %&gt;
    &lt;%= f.input :last_name %&gt;
  
    &lt;%= f.association :recurrents, 
                       as: :check_boxes, 
                       label_method: :description, 
                       value_method: :id,
                       label: 'Recurrent Deductions' %&gt;
  
    &lt;%= f.button :submit, class: 'btn btn-primary' %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>controller</p>
  
  <pre><code>def employee_params
    params.require(:employee).permit(:first_name, :recurrent_ids)
  end
  </code></pre>
  
  <p>here is my edited log</p>
  
  <pre><code>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"=&gt;"✓",       "authenticity_token"=&gt;"IwWzcT2qQJqHkTumWjb3OD5nJe9xLaA+YezMumer9X8=", "employee"=&gt;{"job_id"=&gt;"5", "manager_id"=&gt;"", "first_name"=&gt;"Mark", "recurrent_ids"=&gt;["1", ""]}, "commit"=&gt;"Update Employee", "id"=&gt;"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" = 'mark@yahoo.com' 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)
  </code></pre>