title: permit params array in nested attribute [active admin]
body: <p>How to specify <strong>array attribute of a nested_attribute</strong> in <strong>permit_params</strong> in <strong>active admin</strong>?</p>
  
  <p>app/model/event.rb</p>
  
  <pre><code>class Event &lt; ActiveRecord::Base    
     has_many :other_details, dependent: :destroy    
     accepts_nested_attributes_for :other_details    
  end
  </code></pre>
  
  <p>app/models/other_detail.rb</p>
  
  <pre><code>class OtherDetail &lt; ActiveRecord::Base    
      belongs_to :event    
  end
  </code></pre>
  
  <p>app/admin/event.rb</p>
  
  <pre><code>ActiveAdmin.register Event do    
  permit_params :other_details_attributes =&gt; [:id, :detail_type, :points]    
    form do |f|
      f.inputs do
      f.has_many :other_details do |ff, index|
          ff.input :detail_type
          ff.input :points, input_html: { value: (ff.object.points.join(", ").remove('%') if ff.object.points.present?)}
      end
    end
  end
  </code></pre>
  
  <p>I am getting </p>
  
  <pre><code>params['experience']['other_details_attributes'] = 
  {"0"=&gt;{"detail_type"=&gt;"Itinerary","points"=&gt;"point A, point B", "id"=&gt;"37"},
  "1"=&gt;{"detail_type"=&gt;"Schedule","points"=&gt;"point C, point D", "id"=&gt;"36"}}
  </code></pre>
  
  <p>How to get this?</p>
  
  <pre><code>params['experience']['other_details_attributes'] = 
  {"0"=&gt;{"detail_type"=&gt;"Itinerary", "points"=&gt;["point A", "point B"],"id"=&gt;"37"},
  "1"=&gt;{"detail_type"=&gt;"Schedule", "points"=&gt;["point C", "point D"], "id"=&gt;"36"}}
  </code></pre>
  
  <p><strong>Note</strong> -</p>
  
  <ol>
  <li><p>I am getting <strong>points</strong> in <strong>string</strong> I need it in <strong>array</strong>.</p></li>
  <li><p>I tried method suggested by <strong>@xeon131</strong>, but it led to lots of complicated code for update method. </p></li>
  </ol>