JPA / Hibernate：使用一對多關系映射實體中的單個元素

Question

我有以下表格：

TABLE Orders (
    ID BIGINT NOT NULL PRIMARY KEY,
    ... other columns ...
)

TABLE Order_States (
    ID         BIGINT NOT NULL PRIMARY KEY,
    Order_ID   BIGINT NOT NULL FOREIGN KEY REFERENCES Orders(ID),
    State_Type VARCHAR(30) NOT NULL,
    State_Date DATETIME NOT NULL,
    ... other columns ...
)

以下映射：

@Entity
@Table(name = "orders")
class Order {

    @Id
    @GeneratedValue
    private Long id;

    @OneToMany(mappedBy = "order")
    @OrderBy("stateDate DESC")
    private List<OrderState> orderStates

    public OrderState getCurrentState() {
        return orderStates.get(0);
    }

    public void setCurrentState(OrderState state) {
        state.setStateDate(new Date());
        orderStates.add(state);
    }

    ... other members ...
}

@Entity
@Table(name = "order_states")
class OrderState {

    @Id
    @GeneratedValue
    private Long id;

    @ManyToOne
    @JoinColumn(name = "order_id")
    private Order order;

    @Enumerated(EnumType.STRING)
    @Column(name = "state_type")
    private StateType stateType;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name = "state_date")
    private Date stateDate;

    ... other members ...
}

我不想在我的映射中包含所有訂單的狀態（它們僅僅是出於歷史原因），而只是訂單的當前狀態，這是由最新狀態的日期決定的。

這有什么注釋嗎？ 例如（我猜）：

@Entity
@Table(name = "orders")
class Order {
    ...

    @OneToMany(mappedBy = "order")
    @OrderBy("stateDate DESC")
    @TakeFirst
    private OrderState orderState

    ... getter and setter for orderState ...

    ...
}

Answer 1

您正在談論的功能稱為soft delete 。 下面是一個使用Hibernate的注釋@SQLDelete和@Where來做這些事情的例子。

但是，使代碼工作變得困難

@TakeFirst
private OrderState orderState

像這樣編碼會更容易

@TakeFirst
private Set<OrderState> orderState // this will be a set containing one entry