Active Admin: Form with datepicker on custom page - ruby-on-rails

Question

Alright I made a custom page in Active Admin called "Newest Rooms" and it shows a table with the Hotel Rooms of the current date.
Now I want to add a form the this custom page where I can pick the Date. I've managed to make the form appear with the Datepicker through:
<%= semantic_form_for :newest_rooms, :builder => ActiveAdmin::FormBuilder do |f|
f.inputs do
f.input :Datum, :as => :datepicker
end
f.buttons
end %>
But no idea how to send this to the right controller and to the method HotelRoom.newest_rooms
I hope someone can explain to me how to do this. I've added the code below:
newest_room.rb
ActiveAdmin.register_page "Newest Rooms" do
menu :label => "Newest Rooms"
content do
render "newest_rooms"
end
end
_newest_room.html.erb
<% #cities = Hotel.cities %>
<%= semantic_form_for :newest_rooms, :builder => ActiveAdmin::FormBuilder do |f|
f.inputs do
f.input :Datum, :as => :datepicker
end
f.buttons
end %>
<ul class="room_list">
<% #cities.each do |c| %>
<li>
<table>
<tr>
<td>
<h2><%= c.City %></h2>
</td>
</tr>
<tr class="room_column">
<td>Hotel</td>
<td>Free Rooms</td>
<td>BN-Price</td>
<td>Old Price</td>
</tr>
<% #rooms = HotelRoom.newest_rooms(c.City) %>
<% #rooms.each do |r| %>
<tr>
<td><%= r.hotel.Hotelname %></td>
<td><%= r.FreeRooms %></td>
<td><b><%= r.Price %>€</b></td>
<td><%= r.OldPrice %>€</td>
</tr>
<%end%>
</table>
</li>
<% end %>
</ul>
hotel_room.rb
class HotelRoom < ActiveRecord::Base
validates :title, :presence => true
self.table_name = "hotel_room"
belongs_to :hotel, :foreign_key => 'H_ID'
accepts_nested_attributes_for :hotel
def to_key
[self.ID]
end
def self.newest_rooms(city)
HotelRoom.find(:all, :joins => :hotel, :conditions => ["hotel.City = ? and hotel_room.Date = ?", city, Date.today])
end
end

Answer 1

add an url to your semantic form, like...
<%= semantic_form_for :newest_rooms, :url => hotel_newest_room_path, :builder => ActiveAdmin::FormBuilder do |f| %>