_form.html.erb

<% form_for(@event) do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </p>
  <p>
    <%= f.label :permalink %><br />
    <%= f.text_field :permalink %>
  </p>
  <p>
    <%= f.label :description %><br />
    <%= f.text_area :description %>
  </p>
  <p>
    <%= f.label :start_date %><br />
    <%= f.datetime_text_field :start_date, :blank => true %>
  </p>
  <p>
    <%= f.label :end_date %><br />
    <%= f.datetime_text_field :end_date, :blank => true %>
  </p>
  <p>
    <%= f.label :location %><br />
    <%= f.text_area :location %>
  </p>
  <p>
    <%= f.submit button_name, :class => "button" %>
  </p>
<% end %>

<%= link_to 'Cancel', events_path %>

event.rb

class Event < ActiveRecord::Base
  validates_presence_of :title, :permalink
  validates_datetime :start_date, :allow_nil => true, :allow_blank => true
  validates_datetime :end_date, :allow_nil => true, :allow_blank => true
  
  def to_param
    permalink
  end
end