@Entity
public class User {
	@Id @GeneratedValue
	public long id;
	
	@OneToMany(fetch = FetchType.LAZY, mappedBy = "user", cascade = CascadeType.ALL)
	@MapKeyColumn(name = "name"/*, nullable = true*/)
	public Map<String, UserData> userData = new HashMap<String, UserData>();
}

@Entity
public class UserData {
	@Id @GeneratedValue
	public long id;
	
	@ManyToOne
	public User user;
}

		User user = new User();
//		UserData userData = new UserData();
//		user.userData.put( "foo", userData );
		s.persist( user );
		
		s.flush();
		
		Query q = s.createQuery( "DELETE FROM UserData d WHERE d.user = :user" );
		q.setParameter( "user", user );
		q.executeUpdate();