如果 Address 嵌套在 User 中，为什么我必须保留这两个对象？

我想更好地熟悉 JPA，所以我创建了一个非常简单的项目。我有一个用户类和一个地址类。看来我必须坚持两者，即使我将地址添加到我的用户类中？

User:

import javax.persistence.*;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

@Entity
@Table(name = "usr") // @Table is optional, but "user" is a keyword in many SQL variants 
@NamedQuery(name = "User.findByName", query = "select u from User u where u.name = :name")
public class User {
    @Id // @Id indicates that this it a unique primary key
    @GeneratedValue // @GeneratedValue indicates that value is automatically generated by the server
    private Long id;

    @Column(length = 32, unique = true)
    // the optional @Column allows us makes sure that the name is limited to a suitable size and is unique
    private String name;

    // note that no setter for ID is provided, Hibernate will generate the ID for us

    @OneToMany(fetch=FetchType.LAZY, mappedBy="user")
    private List<Address> addresses;

Address:

@Entity
public class Address {

    @Id // @Id indicates that this it a unique primary key
    @GeneratedValue // @GeneratedValue indicates that value is automatically generated by the server
    private Long id;

    @Column(length=50)
    private String address1;

    @ManyToOne
    @JoinColumn(name="user_id")
    private User user;

实体管理器：

EntityManager entityManager = Persistence.createEntityManagerFactory("tutorialPU").createEntityManager();

entityManager.getTransaction().begin();

User user = new User();
user.setName("User");

List<Address> addresses = new ArrayList<Address>();
Address address = new Address();
address.setAddress1("Address1");

addresses.add(address);
user.setAddresses(addresses);
entityManager.persist(user);
entityManager.persist(address);
entityManager.getTransaction().commit();
entityManager.close();

可能做错了什么......只是不确定它是什么？

任何建议，将不胜感激。

Thanks,

S

Try the cascade注释的元素。

@OneToMany(fetch=FetchType.LAZY, mappedBy="user", cascade=CascadeType.PERSIST) 
private List<Address> addresses; 

The 文档 http://docs.oracle.com/javaee/6/api/index.html?javax/persistence/OneToMany.html表示默认情况下不进行级联操作。它还指出级联操作是可选的，因此它实际上取决于您正在使用的实现。

另外，在设置关系时，请确保设置关系的双方。将地址设置为用户并将用户设置为地址。