gistfile1.rhtml

<!-- This gets the error:
 "undefined method `merge' for :code:Symbol"
-->
<%=  f.collection_select(:section, :assessment_id, Assessment.all, :id, :code) %>


<!-- but building it manually works fine: --> 

    <select name="section[assessment_id]">
      <% Assessment.all.each do |a| %>
        <option value="<%= a.id %>"><%= a.code %></option>
      <% end %>
    </select>