@SuppressWarnings("serial")
@org.hibernate.annotations.AccessType("property")
@Embeddable
public class RecipientPK implements Serializable {

   private long ticketId;
   private long userId;

   public RecipientPK() {
      super();
   }

   @ManyToOne
   public long getTicketId() {
      return ticketId;
   }

   public void setTicketId(long ticketId) {
      this.ticketId = ticketId;
   }

   public long getUserId() {
      return userId;
   }

   public void setUserId(long userId) {
      this.userId = userId;
   }

   public boolean equals(Object o) {
   ...
   }

   public int hashCode() {
   ...
   }
}

@Entity
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
@org.hibernate.annotations.AccessType("property")
public class Recipient extends IdentityData {
   
   public enum RecipientType {TO, CC, BCC}
   
   private RecipientPK id;
   private RecipientType recipientType;

   public Recipient() {
      super();
   }

   @EmbeddedId
   public RecipientPK getId() {
      return id;
   }
   public void setId(RecipientPK id) {
      this.id = id;
   }
   
   public RecipientType getRecipientType() {
      return recipientType;
   }
   public void setRecipientType(RecipientType recipientType) {
      this.recipientType = recipientType;
   }
   
}

   public enum TicketType { USER_TO_USER, USER_TO_SYSTEM }
   
   public enum TicketStatus { OPEN, CLOSED }
   
   public enum Urgency { NORMAL, URGENT }
   
   
   // unique ticket id
   private long id;
   // the parent ticket. 0=no parent
   private long parentTicketId;
   // userId who opened the ticket
   private long userId;
   private TicketType ticketType;
   private TicketStatus ticketStatus;
   private Urgency urgency;
   private String subject;
   private String body;
   // the labels this ticket belongs to
//   private Set<Label> labels;
   private Set<Recipient> recipients;
      
   public Ticket() {
      super();
   }
   
   public Ticket(long id, long parentTicketId, long userId, TicketType ticketType,
         TicketStatus ticketStatus, Urgency urgency, String subject, String body) {
      super();
      this.id = id;
      this.parentTicketId = parentTicketId;
      this.userId = userId;
      this.ticketType = ticketType;
      this.ticketStatus = ticketStatus;
      this.urgency = urgency;
      this.subject = subject;
      this.body = body;
   }
   @Id
   @GeneratedValue(strategy = GenerationType.AUTO)
   public long getId() {
      return id;
   }
   public void setId(long id) {
      this.id = id;
   }

   ... getters & setters here ....

   @OneToMany(mappedBy="ticketId")
   @Cascade(org.hibernate.annotations.CascadeType.DELETE_ORPHAN)
   public Set<Recipient> getRecipients() {
      return recipients;
   }

   public void setRecipients(Set<Recipient> recipients) {
      this.recipients = recipients;
   }

@Embeddable
public abstract class IdentityData {
   // date row created
   private Date createDate;
   // timestamp: row changed
   private Date updateDate;
   // ID of user last modified the row
   private long operatorId;
   // IP of user last modified the row
   private String operatorIp;

   public IdentityData() {
      super();
   }

   ... getters & setters here ....

@CollectionOfElements

@ManyToOne

...
@CollectionOfElements(fetch = FetchType.EAGER)
   public Set<RecipientElement> getRecipients() {
      return this.recipients;
   }
...

@Embeddable
public class RecipientElement implements java.io.Serializable {
...