app/views/admin/calendars/edit.html.erb
<h1>Edit Calendar</h1>
<%= simple_form_for @calendar, url: admin_calendar_path(@calendar), method: :put do |form| %>
<% if @calendar.school? %>
<%= form.input :based_on_id, as: :select, collection: Calendar.regional, include_blank: false %>
<% elsif @calendar.regional? %>
<%= form.input :based_on_id, as: :select, collection: Calendar.national, include_blank: false %>
<% end %>
<%= form.input :title, as: :string %>
<%= form.button :submit, 'Update Calendar' %>
<% end %>