JPA - @MapKeyJoinColumn Examples

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @ElementCollection
    @CollectionTable(name = "EMP_TASKS", joinColumns = @JoinColumn(name = "EMP_ID"))
    @MapKeyJoinColumn(name = "TASK_ID")
    @Column(name = "TASK_DATE")
    private Map<Task, Date> taskMap;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    .............
}