JPA - @MapKeyColumn Examples

@Entity
public class Customer {
    @Id
    @GeneratedValue
    private int id;

    private String name;
    @ElementCollection
    @MapKeyColumn(name = "item")
    @Column(name = "qty")
    @CollectionTable(name = "ITEM_QTY")
    private Map<String, Integer> itemQtyMap;
    .............
}

@Entity
public class Customer {
    @Id
    @GeneratedValue
    private int id;
    private String name;
    @ElementCollection
    @CollectionTable(name = "ORDERS")
    @MapKeyColumn(name = "TYPE")
    private Map<String, Order> orderMap;
    .............
}

@Embeddable
public class Order {
    private String item;
    private int qty;
    private Date date;
    .............
}

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany
    @JoinTable(name = "ASSIGNED_TASKS",
            joinColumns = {@JoinColumn(name = "EMPLOYEE_FK")},
            inverseJoinColumns = {@JoinColumn(name = "TASK_FK")})
    @MapKeyColumn(name = "TASK_DATE")
    private Map<Date, Task> tasks;
    .............
}

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

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany
    @JoinColumn(name = "EMPLOYEE_FK")
    @MapKeyColumn(name = "TASK_DATE", nullable = true)
    private Map<Date, Task> tasks;
    .............
}

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

@Entity
public class Employee {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    @OneToMany(mappedBy = "taskEmployee", cascade = CascadeType.ALL)
    @MapKeyColumn(name = "TASK_DATE", nullable = true)
    private Map<Date, Task> tasks;
    .............
}

@Entity
public class Task {
    @Id
    @GeneratedValue
    private long id;
    private String name;
    private String description;
    @ManyToOne
    @JoinColumn(name = "EMP_FK")
    private Employee taskEmployee;
    .............
}