title: Active Admin image upload
body: <p>I'm new ruby and ruby on rails. I want image upload with active admin <br> I follow this code
  <br>
  app\admin\book.rb
  ActiveAdmin.register Book do</p>
  
  <pre><code># See permitted parameters documentation:
  # https://github.com/activeadmin/activeadmin/blob/master/docs/2-resource-customization.md#setting-up-strong-parameters
  #
   permit_params :list, :of, :attributes, :on, :model
  #
  # or
  #
  # permit_params do
  #   permitted = [:permitted, :attributes]
  #   permitted &lt;&lt; :other if resource.something?
  #   permitted
  # end
  index do
    column :name
    column :image
  
  
    column :author
    column :genre
    column :price
    actions
  end
  form :html =&gt; { :enctype =&gt; "multipart/form-data" } do |f|
     f.inputs "Details" do
      f.input :image, :as =&gt; :file, :hint =&gt; f.template.image_tag(f.object.image.url(:medium))
      f.input :author
      f.input :name
    end
    f.actions
   end
  end
  </code></pre>
  
  <p>And<br>
  app\models\book.rb</p>
  
  <pre><code>class Book &lt; ActiveRecord::Base
    belongs_to :author
    belongs_to :genre
  has_attached_file :image, :styles =&gt; { :medium =&gt; "238x238&gt;", 
                                     :thumb =&gt; "100x100&gt;"
                                   }
  end
  </code></pre>
  
  <p>Yes i see file upload button in create page. But don't save form.<br></p>