@Entity
public class ContactEntity
{
...

   private Collection<EventInstanceEntity> eventInstances;

   @JoinTable(name = "contact_event", catalog = "kbc", joinColumns = @JoinColumn(name = "contact_id"), inverseJoinColumns = @JoinColumn(name = "event_id"))
   @ManyToMany
   public Collection<EventInstanceEntity> getEventInstances()
   {
      return eventInstances;
   }

   public void setEventInstances(Collection<EventInstanceEntity> eventInstances)
   {
      this.eventInstances = eventInstances;
   }

...
}

@Entity
public class EventInstanceEntity
{
...

   private int eventId;

   @Column(name = "event_id")
   @Basic
   public int getEventId()
   {
      return eventId;
   }

   public void setEventId(int eventId)
   {
      this.eventId = eventId;
   }
...