复合主键 Hibernate 和 Java 实现

Question

我定义了一个非常简单的数据库，如下所示：

我正在使用 hibernate 插件来生成不同的数据库类，包括客户和订单之间的一对多关系。我将这种关系作为一种识别关系，因为如果没有链接到客户，订单就不会存在。

我有以下三个课程：

=>类客户

private int idCustomer;
private String name;
private Set<Order> orders = new HashSet<Order>(0);

public Customer() {
}

public Customer(int idCustomer) {
    this.idCustomer = idCustomer;
}

public Customer(int idCustomer, String name, Set<Order> orders) {
    this.idCustomer = idCustomer;
    this.name = name;
    this.orders = orders;
}

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "idCustomer", unique = true, nullable = false)
public int getIdCustomer() {
    return this.idCustomer;
}

public void setIdCustomer(int idCustomer) {
    this.idCustomer = idCustomer;
}

@Column(name = "name", length = 45)
public String getName() {
    return this.name;
}

public void setName(String name) {
    this.name = name;
}

@OneToMany(fetch = FetchType.LAZY, mappedBy = "customer")
public Set<Order> getOrders() {
    return this.orders;
}

public void setOrders(Set<Order> orders) {
    this.orders = orders;
}

=>班级顺序：

private OrderId id;
private Customer customer;
private String quantity;
private Float price;

public Order() {
}

public Order(OrderId id, Customer customer) {
    this.id = id;
    this.customer = customer;
}

public Order(OrderId id, Customer customer, String quantity, Float price) {
    this.id = id;
    this.customer = customer;
    this.quantity = quantity;
    this.price = price;
}

@EmbeddedId
@AttributeOverrides({
        @AttributeOverride(name = "idOrder", column = @Column(name = "idOrder", nullable = false)),
        @AttributeOverride(name = "customerIdCustomer", column = @Column(name = "Customer_idCustomer", nullable = false)) })
public OrderId getId() {
    return this.id;
}

public void setId(OrderId id) {
    this.id = id;
}

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "Customer_idCustomer", nullable = false, insertable = false, updatable = false)
public Customer getCustomer() {
    return this.customer;
}

public void setCustomer(Customer customer) {
    this.customer = customer;
}

@Column(name = "quantity", length = 45)
public String getQuantity() {
    return this.quantity;
}

public void setQuantity(String quantity) {
    this.quantity = quantity;
}

@Column(name = "price", precision = 12, scale = 0)
public Float getPrice() {
    return this.price;
}

public void setPrice(Float price) {
    this.price = price;
}

=> Class OrderId

private int idOrder;
private int customerIdCustomer;

public OrderId() {
}

public OrderId(int idOrder, int customerIdCustomer) {
    this.idOrder = idOrder;
    this.customerIdCustomer = customerIdCustomer;
}

@Column(name = "idOrder", nullable = false)
public int getIdOrder() {
    return this.idOrder;
}

public void setIdOrder(int idOrder) {
    this.idOrder = idOrder;
}

@Column(name = "Customer_idCustomer", nullable = false)
public int getCustomerIdCustomer() {
    return this.customerIdCustomer;
}

public void setCustomerIdCustomer(int customerIdCustomer) {
    this.customerIdCustomer = customerIdCustomer;
}

public boolean equals(Object other) {
    if ((this == other))
        return true;
    if ((other == null))
        return false;
    if (!(other instanceof OrderId))
        return false;
    OrderId castOther = (OrderId) other;

    return (this.getIdOrder() == castOther.getIdOrder())
            && (this.getCustomerIdCustomer() == castOther
                    .getCustomerIdCustomer());
}

public int hashCode() {
    int result = 17;

    result = 37 * result + this.getIdOrder();
    result = 37 * result + this.getCustomerIdCustomer();
    return result;
}

然后我有我的主类：

public static void main(String[] args) {
    Customer customer = new Customer();
    customer.setName("John Doe");
    CustomerDAO.save(customer);

    Order order = new Order();
    order.setQuantity(10);
    order.setPrice(100);
    order.setCustomer(customer);

    OrderDAO.save(order);

}

请注意，我的 DAO 对象没有做任何花哨的事情...只是获取会话的常用 HibernateUtil 实现并最终调用“保存”方法。我的问题如下。我以前从未处理过复合键...请提前原谅我的愚蠢问题。我不想手动处理不同的 id 和主键。对于 Cutomer 类，这不是问题，因为我设置了一个策略，在保存到数据库时会自动创建 id。对于 Order 类，我也不想处理这个问题。但由于密钥是复合的，Hibernate 在尝试将此对象保存在数据库中时会生成一个identifierGenerationExeption...我想要的是以下 =>自动生成的订单 ID，因为我在订单对象中设置了客户，所以我希望 Hibernate 将客户 ID 链接到组合键中的 ID...执行此操作的正确方法是什么？

谢谢

Answer 1

为什么要在 Order 实体的主键中包含客户 ID 外键？它的主键应该是idOrder。 Customer_idCustomer 应该是外键，并且不应该是订单 ID 的一部分。

Answer 2

不鼓励使用复合键，并且仅应在被迫时使用（例如：遗留数据库）。我认为您应该将订单中的 Customer_id 设置为 not null。订单有一个简单、常规的 ID (idOrder)，一切都应该很简单。