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Question

我有2个表email_address和group_email

我想获取一个电子邮件地址列表，如果是组，还会列出组的电子邮件。这是我的hibernate dom对象：

@Entity
@Table(name = "email_address")
public class EmailAddressDom {

@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "email_address_id_seq")
@SequenceGenerator(name = "email_address_id_seq", sequenceName = "email_address_id_seq")
private int id;

@Column(name = "name")
private String name;

@Column(name = "email")
private String email;

@Column(name = "is_group")
private boolean isGroup;

@Column(name = "status")
private boolean status;
// Getters and setters

以下是我如何获取列表的实现

public List<EmailAddressDom> getEmailAddresses() {
    Session session = getCurrentSession();
    Criteria criteria = session.createCriteria(EmailAddressDom.class);
    List<EmailAddressDom> emailAddresses = criteria.list();
    return emailAddresses;
}

结果是

[
  {
    "id": 451,
    "name": "HS",
    "isGroup": true,
    "status": true
  },
  {
    "id": 452,
    "name": "test4",
    "email": "test4@mail.com",
    "isGroup": false,
    "status": true
  },
  {
    "id": 450,
    "name": "test3",
    "email": "test3@mail.com",
    "isGroup": false,
    "status": true
  },
  {
    "id": 402,
    "name": "test2",
    "email": "test2@mail.com",
    "isGroup": false,
    "status": true
  },
  {
    "id": 401,
    "name": "test1",
    "email": "test1@mail.com",
    "isGroup": false,
    "status": true
  }
]

我想得到像这样的结果

[
   {
      "id":451,
      "name":"HS",
      "isGroup":true,
      "status":true,
      "groupEmails":[
         {
            "id":450,
            "name":"test3",
            "email":"test3@mail.com",
            "isGroup":false,
            "status":true
         },
         {
            "id":452,
            "name":"test4",
            "email":"test4@mail.com",
            "isGroup":false,
            "status":true
         }
      ]
   },
   {
      "id":402,
      "name":"test2",
      "email":"test2@mail.com",
      "isGroup":false,
      "status":true
   }
]

我应该在EmailAddressDom实体中使用哪种映射？

根据评论更新

我已经按照以下方式编写了一个简单的应用程序映射，并且工作正常

@ManyToMany(fetch= FetchType.EAGER, cascade={CascadeType.ALL})
    @JoinTable(name="group_email",
       joinColumns={@JoinColumn(name="group_id")},
       inverseJoinColumns={@JoinColumn(name="email_addr_id")})
private List<EmailAddressDom> groupEmails;

但是我很困惑在我的网络应用程序中设置它，它抛出以下异常：

Association has already been visited: AssociationKey(table=group_email, columns={email_addr_id})

可能是什么原因？

Answer 1

要实现自我加入，请在EmailAddressDom类中添加对自己的引用，如：

    @OneToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "group_email", 
        joinColumns = @JoinColumn(name = "email_addr_id", referencedColumnName = "id"),
        inverseJoinColumns=@JoinColumn(name="group_id", referencedColumnName="id" ))
    private List<EmailAddressDom> emailAddressDoms;

在group_email表格中，您不需要id列email_addr_id和group_id组合是唯一的，或者您是否在群组中多次允许同一封电子邮件？< / p>

OP发表评论后更新： 要按电子邮件组进行分组，请更改映射，如下所示。

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinTable(name = "group_email", 
        joinColumns = @JoinColumn(name="group_id", referencedColumnName="id" ),
        inverseJoinColumns=@JoinColumn(name = "email_addr_id", referencedColumnName = "id"))
    private List<EmailAddressDom> emailAddressDoms;

Answer 2

要么加载

@OneToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "group_email", 
        joinColumns = @JoinColumn(name = "email_addr_id", referencedColumnName = "id"),
        inverseJoinColumns=@JoinColumn(name="group_id", referencedColumnName="id" ))
    private List<EmailAddressDom> emailAddressDoms;

OR

//明确加入条件

public List<EmailAddressDom> getEmailAddresses() {
Session session = getCurrentSession();
Criteria criteria = session.createCriteria(EmailAddressDom.class);
criteria.setFetchMode("emailAddressDoms", fetchMode.JOIN);
List<EmailAddressDom> emailAddresses = criteria.list();
return emailAddresses;

}