订单到行项目的JPA映射

Question

我声明了一个订单实体。它由日期、客户和LineItem对象列表组成。

行项目具有产品和数量的属性。我正试图模拟与JPA的这种关系。每个行项目都有ID似乎不正确，但我不确定如何在JPA中表达行项目和订单之间的关系：

@Entity
@Table(name = "ORDERS")
public class Order {
   @Id
   @GeneratedValue(strategy = GenerationType.AUTO, generator = "cust_seq_gen")
   @SequenceGenerator(name = "cust_seq_gen", sequenceName = "CUSTOMER_SEQUENCE", allocationSize = 5)
   private int id;
   @Temporal(DATE)
   @Column(name = "DATE_PLACED")
   private Date datePlaced;
   @Enumerated(EnumType.STRING)
   @Column(name = "STATUS")
   private Status status;
   @JoinTable(
        name = "LINE_ITEM_JOIN",
        joinColumns = @JoinColumn(name = "ORDER_ID"),
        inverseJoinColumns = @JoinColumn(name = "LINE_ITEM_ID")
   )
   private List<LineItem> orderSegments;
   @Column(name = "TOTAL", precision = 10, scale = 2)
   private double total;
   @ManyToOne
   private Customer customer;
   @Column(name = "NOTES")
   private String notes;
   }

LineItem类

@Entity
@Table(name = "LINE_ITEMS")
public class LineItem {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO, generator = "line_item_seq_gen")
  @SequenceGenerator(name = "line_item_seq_gen", sequenceName = "LINE_ITEM_SEQUENCE",   allocationSize = 5)
  private Order associatedOrder;
  private Product product;
  private int quantity;
  ...
}

我认为行项目的主键应该是产品id、数量和订单id的组合，尽管我知道我没有对此建模。

Answer 1

通过将行项目定义为嵌入集合，也可以忽略行项目的id。例如

public class Order {

     @ElementCollection @OrderColumn
     private List<LineItem> orderSegments = new ArrayList<>();

}

@Embeddable
public class LineItem {

     @ManyToOne
     private Product product;

     private int quantity;

}

这样您将无法直接通过它们的id检索LineItem。您需要order来获取或添加LineItem。