title: form_for 'file_field' not showing file chosen in edit action
body: <p>I am using <code>file_field</code> and it is working fine on creation - file is getting saved. But when I'm doing edit of the same record <code>no file chosen</code> is coming.</p>
  
  <p>I have created partial form which I am using in new and edit actions. When I am clicking on edit option of a record all other fields are coming pre-selected but file is not coming.</p>
  
  <pre><code># edit.html.erb
  &lt;h3&gt;Order Detail&lt;/h3&gt;
  &lt;div id="field"&gt;
    &lt;div id="field0"&gt;
      &lt;%= render 'form', order_detail: @order_detail %&gt;
    &lt;/div&gt;
  &lt;/div&gt;   
  
  # _form.html.erb
  &lt;%= form_for @order_detail do |f| %&gt; 
    &lt;div class="form-group required"&gt;
      &lt;label class="col-md-4 control-label" for="action_id"&gt;Delivery Date&lt;/label&gt;  
      &lt;div class="col-md-5"&gt;
        &lt;%=f.text_field :delivery_date, "data-provide" =&gt; 'datepicker', class: 'form-control input-md datepicker',id: 'selectDate2',placeholder: "Delivery date(yyyy-mm-dd)" ,required: true%&gt;
      &lt;/div&gt;
    &lt;/div&gt;
    &lt;div class="form-group required"&gt;
      &lt;label class="col-md-4 control-label" for="action_id"&gt;Pdf File&lt;/label&gt;  
      &lt;div class="col-md-5"&gt;
        &lt;%=f.file_field :pdf_file, class: 'form-control input-md' ,required: true%&gt;
      &lt;/div&gt;
    &lt;/div&gt;
    &lt;div class="actions"&gt;
      &lt;%= submit_tag "Submit",class:"btn btn-success" ,remote: true%&gt;
    &lt;/div&gt;
  &lt;%end%&gt;
  </code></pre>
  
  <p>I am expecting file chosen should come but it's not coming as it is stored in database.</p>