java - 一个用户在mysql数据库中可以有多条消息

Question

我正在尝试使用 Hibernate 在用户表和消息表之间创建一对多关系。一个用户可以在消息数据库中拥有多条消息。但是，我无法获得它的架构。这是我的代码

用户.java

@Entity
@Table
public class User {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private Long id;

    @ManyToOne
    User user;
    @Column(unique = true)
    private String username;
    private String password;

    @OneToMany
    Message message;

    public User(String userName, String password) {
        this.username = userName;
        this.password = password;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }


    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }

    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
}

消息.java

@Entity
public class Message {

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String sender;
    private String receiver;
    private String content;

    @Type(type="timestamp")
    private Date created;

    public Message() {

    }

    public Message(String sender, String receiver, String content) {
        this.sender = sender;
        this.receiver = receiver;
        this.content = content;
        this.created = new Date();
    }

    public Date getCreated() {
        return created;
    }

    public void setCreated(Date created) {
        this.created = created;
    }

    public int getId() {
        return id;
    }

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

    public String getSender() {
        return sender;
    }

    public void setSender(String sender) {
        this.sender = sender;
    }

    public String getReceiver() {
        return receiver;
    }

    public void setReceiver(String receiver) {
        this.receiver = receiver;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}

这是我的架构

CREATE TABLE `Message` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `content` varchar(255) DEFAULT NULL,
  `created` datetime DEFAULT NULL,
  `receiver` varchar(255) DEFAULT NULL,
  `sender` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=33 DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `User` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `password` varchar(255) DEFAULT NULL,
  `username` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UK_jreodf78a7pl5qidfh43axdfb` (`username`)
) ENGINE=InnoDB AUTO_INCREMENT=20 DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;

但不幸的是，我无法获得用户和消息的一对多关系。谁能帮我做一下。如何设计一个模式来获得一对多关系以及如何更改 POJO 类来实现它？

Answer 1

您正在以错误的方式实现 OneToMany 关系，您应该在 User 实体中使用消息的 Collection

@OneToMany
private List<Messages> messages;  // Or Set<>