@SuppressWarnings("serial")
@Entity
@Table(name = "patient_data")
public class Patient_data {

   private int _patient_id;
   private String _name;
   private String _firstname;
   private String _location;
   private String _street;
   private Date _date_of_birth;
   private String _gender;
   private float _weight;
   private float _bodysize;
   
// Objects for interpreter, assigner
   private Client _interpreter;
   private Client _assigner;
   
//    Getter/Setter patient_id -> PK
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
   public int getPatient_id(){
      return _patient_id;
   }

   public void setPatient_id(int patient_id){
      _patient_id = patient_id;
   }

//    Getter/Setter interpreter -> FK
   @ManyToOne
   @JoinColumn(name="interpreter")
   public Client getInterpreter(){
      return _interpreter;
   }

   public void setInterpreter(Client interpreter){
      _interpreter = interpreter;
   }   
   
//    Getter/Setter assigner -> FK
   @ManyToOne
   @JoinColumn(name="assigner")
   public Client getAssigner(){
      return _assigner;
   }

   public void setAssigner(Client assigner){
      _assigner = assigner;
   }   
      
   ....

   }      

//Initialisierung ...

Patient p = new Patient();

// setze Properties von Patient
...

p.setAssigner(new Client());

em.persist(p);
/**
* Problem, da Client noch nicht persistent ist. Hibernate weiß nicht,
* welchen Foreign Key es im Patienten-Satz setzen soll
*/