java - Entity-Bean (JPA) 中的单向关系

Question

如何在 EJB 3.0 Entity-Beans (JPA) 中创建单向关系？

例如，客户知道订单，但订单没有客户的任何方法。使用(@OneToMany 或@OneToOne 或@ManyToMany)

问候

Answer 1

下面是使用 JPA 2.0 建立单向 @OneToMany 关系的方法:

@Entity
public class Customer {
  @Id
  @Column(name="cust_id")
  private long id;
  ...
  @OneToMany
  @JoinColumn(name="owner_id", referencedColumnName="cust_id")
  private List<Order> order;
  ...
}

@Entity
public class Order {
    @Id
    @Column(name="order_id")
    private long id;
    ...
}

关系数据库:

客户:

+---------+---------+------+-----+---------+-------+
| Field   | Type    | Null | Key | Default | Extra |
+---------+---------+------+-----+---------+-------+
| cust_id | int(11) | NO   | PRI | NULL    |       |
+---------+---------+------+-----+---------+-------+

顺序:

+----------+---------+------+-----+---------+-------+
| Field    | Type    | Null | Key | Default | Extra |
+----------+---------+------+-----+---------+-------+
| order_id | int(11) | NO   | PRI | NULL    |       |
| owner_id | int(11) | NO   | MUL | NULL    |       |
+----------+---------+------+-----+---------+-------+