Customizing the Form

Active Admin gives you complete control over the output of the form by creating a thin DSL on top of Formtastic:

ActiveAdmin.register Post do

  form do |f|
    f.inputs 'Details' do
      f.input :title
      f.input :published_at, label: "Publish Post At"
      f.input :category
    end
    f.inputs 'Content', :body
    f.actions
  end

end

Please view the documentation for Formtastic to see all the wonderful things you can do.

Partials

If you require a more custom form than the DSL can provide, use a partial instead:

ActiveAdmin.register Post do
  form partial: 'form'
end

Which looks for something like this:

<%# app/views/admin/posts/_form.html.erb %>
<%= semantic_form_for [:admin, @post] do |f| %>
  <%= f.inputs :title, :body %>
  <%= f.actions do %>
    <%= f.action :submit %>
    <li class="cancel"><%= link_to 'Cancel', collection_path %></li>
  <% end %>
<% end %>

Nested Resources

You can create forms with nested models using the has_many method:

ActiveAdmin.register Post do

  form do |f|
    f.inputs 'Details' do
      f.input :title
      f.input :published_at, label: 'Publish Post At'
    end
    f.inputs 'Content', :body
    f.inputs do
      f.has_many :categories, heading: 'Themes', allow_destroy: true, new_record: false do |a|
        a.input :title
      end
    end
    f.inputs do
      f.has_many :taggings, sortable: :position do |t|
        t.input :tag
      end
    end
    f.inputs do
      f.has_many :comment, new_record: 'Leave Comment' do |b|
        b.input :body
      end
    end
    f.actions
  end

end

The :allow_destroy option adds a checkbox to the end of the nested form allowing removal of the child object upon submission. Be sure to set allow_destroy: true on the association to use this option.

The :heading option adds a custom heading. You can hide it entirely by passing false.

The :new_record option controls the visibility of the new record button (shown by default). If you pass a string, it will be used as the text for the new record button.

The :sortable option adds a hidden field and will enable drag & drop sorting of the children. It expects the name of the column that will store the index of each child.

Datepicker

ActiveAdmin offers the datepicker input, which uses the jQueryUI datepicker. The datepicker input accepts any of the options available to the standard jQueryUI Datepicker. For example:

form do |f|
  f.input :starts_at, as: :datepicker, datepicker_options: { min_date: "2013-10-8",        max_date: "+3D" }
  f.input :ends_at,   as: :datepicker, datepicker_options: { min_date: 3.days.ago.to_date, max_date: "+1W +5D" }
end

Displaying Errors

To display a list of all validation errors:

form do |f|
  f.semantic_errors *f.object.errors.keys
  f.inputs
  f.actions
end

This is particularly useful to display errors on virtual or hidden attributes.