@Entity
@Table(name = "USR_USER")
public class User extends PersistentObject {

   [...]

   @Any(metaColumn = @Column(name = "USR_OWNERTYPE"))
   @AnyMetaDef(idType = "long", metaType = "string", metaValues = {
         @MetaValue(targetEntity = Customer.class, value = "CST"),
         @MetaValue(targetEntity = Client.class, value = "CLT") })
   @JoinColumn(name = "USR_OWNERID")
   private PersistentObject owner;
}

@Entity
@Table(name = "CST_CUSTOMER")
public class Customer extends PersistentObject {

   @Id
   @GeneratedValue
   @Column(name="CST_ID")
   private long id;

   [...]

   // @OneToMany(mappedBy = "owner")
   private transient Set<User> users;
}

Caused by: org.hibernate.MappingException: Foreign key (FK35B91BB65D577CEF:USR_USER [USR_OWNERTYPE,USR_OWNERID])) must have same number of columns as the referenced primary key (CST_CUSTOMER [CST_ID])