1 => Для GET request
использовать method: :get
2 => Для Ajax представить использовать :remote => true
<%= form_for @object, url: create_object_path, :remote => true, method: :get do |f| %>
<%=f.text_field :field_1%>
<%=f.text_field :field_2%>
<%=f.text_field :field_3%>
<%= f.hidden_field :another_field, :value @hpentry.HPEntry_Id.present? ? @hpentry.HPEntry_Id : nil%>
<%=f.submit :submit%>
<%end%>