title: Rails ActiveAdmin. How to set default value?
body: <p>I have code like this:</p>
  
  <pre><code>ActiveAdmin.register Post do
  
  form do |f|
    f.inputs "Post Details" do
      f.input :title
      f.input :body
      f.input :published_at, :as =&gt; DateTime.now
    end
    f.actions
  end
  </code></pre>
  
  <p>I want the field <code>:published_at</code> (which is t.datetime) to be set to the current date and time by default. My example doesn't work. How can I achieve this?</p>