@Entity
 public class Questionarie {

 @ManyToOne(optional=true)
private OptionGroup optionGroup;

<field:select  field="optionGroup" id="c_com_simplemed_npc_domain_Questionarie_optionGroup" itemValue="id" items="${optiongroups}" path="/optiongroups" z="oC8yt64jJ8W3Blyj4gQxDWOOGR8="/>