Question

我一直在使用hibernate创建复合键。我找到了这个链接： how to make a composite primary key (java persistence annotation)

首先，我用@NaturalId尝试了Tim接受的解决方案。没有为我工作。

其次，我尝试了Arthur Ronald F D Garcia的解决方案。我仍然遇到一些问题。这是我的代码，与Arthur Ronald F D Garcia的解决方案非常相似。

邮箱类：

@Entity
public class Mailbox {

    @Id
    @GeneratedValue
    private int mailboxId;
    @Column( unique=true, nullable=false )
    private String name;    
    @Column( unique=true, nullable=false )
    private String employeeId;  
    private String status;
    private Date createdOn;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="joinedMailboxMessageId.mailboxId")
    private List<MailboxMessages> joinedMailboxMessageList = new ArrayList<MailboxMessages>();

    public Mailbox(){}
    public Mailbox(int id)  {this.mailboxId=id;}
    public void addSMail(SMail mail) {
        // Implementation
    }
    //Getters and setters
}

SMail课程

@Entity
public class SMail {

    @Id
    @GeneratedValue
    private int messageId;

    private Date originDate;
    private String from;
    @ElementCollection
    private List<String> to=new ArrayList<String>();
    @Lob
    private String message;
    private String subject;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="joinedMailboxMessageId.messageId")
    private List<MailboxMessages> joinedMailboxMessageList = new ArrayList<MailboxMessages>();

    public SMail() {}
    public SMail(int messageId) {
        this.messageId=messageId;
    }

    // addMailbox sets up bidirectional relationship
    public void addMailbox(Mailbox mailbox) { // Implementation}
//Getters and setters
}

最后我的MailboxMessages类

@Entity
public class MailboxMessages {

    @ManyToOne
    @JoinColumn(name="MAILBOX_ID", insertable=false, updatable=false)
    private Mailbox mailboxId;

    @ManyToOne
    @JoinColumn(name="MESSAGE_ID", insertable=false, updatable=false)
    private SMail messageId;

    private boolean read;
    private boolean deleted;
    private boolean flagged;
    private String priority;
    private Date messageDate;

    @EmbeddedId
    // Implemented as static class - see bellow
    private MailboxMessagesId joinedMailboxMessageId;

    // INNER CLASS: required because this class contains composite id
    @Embeddable
    public static class MailboxMessagesId implements Serializable {

    @ManyToOne
        @JoinColumn(name="MAILBOX_ID")
        private Mailbox mailboxId;

        @ManyToOne
        @JoinColumn(name="MESSAGE_ID")
        private SMail messageId;

        // required no arg constructor
        public MailboxMessagesId() {}

        public MailboxMessagesId(Mailbox mailbox, SMail mail) {
            this.mailboxId = mailbox;
            this.messageId = mail;
        }

        public MailboxMessagesId(int mailboxId, int messageId) {
            this(new Mailbox(mailboxId), new SMail(messageId));
        }

        @Override
        public boolean equals(Object instance) {
            if (instance == null)
                return false;

            if (!(instance instanceof MailboxMessagesId))
                return false;

            final MailboxMessagesId other = (MailboxMessagesId) instance;

            if (!(mailboxId.getMailboxId()==(other.getMailboxId().getMailboxId())))
                return false;

            if (!(messageId.getMessageId()==(other.getMessageId().getMessageId())))
                return false;

            return true;
        }

        @Override
        public int hashCode() {
            int hash = 7;
            hash = 47 * hash + (this.mailboxId != null ? this.mailboxId.hashCode() : 0);
            hash = 47 * hash + (this.messageId != null ? this.messageId.hashCode() : 0);
            return hash;
        }

        //Getters and setters
    }
    //Constructors and getters and setters
}

现在真正的问题是hibernate只为邮箱类创建表。所以我想问题可能在其他2个类中。我尝试了亚瑟·罗纳德的确切解决方案;它工作得很好。你能帮我辨别一下我在代码中可能犯的错误吗？此外，如果在MailboxMessage类中创建复合键的技术有替代方法

EDIT1：

发现的问题之一是我使用'from'作为我的成员字段，它是sql的保留关键字。谁会想到这个？但问题仍然存在。现在我有一个用于smail类的表，但仍然没有为MailboxMessages类创建表。请帮帮我。

Answer 1

我认为这是解决方案，例如字段名称只是示例：

@Id
@Column(name = "EMP_NO_FK" , unique=true , nullable = false ,length=10)
private Long empno;

@Id
@Column(name = "GROUP_NO_FK" , unique=true , nullable = false ,length=5)
private Long  groupNo;

@Id
@Column(name = "DEPT_NO_FK" , unique=true , nullable = false ,length=10)
private Long deptno;

@Id
@Column(name = "YEAR_NAME_M_FK" , unique=true , nullable = false ,length=4)
private Integer  year;

Answer 2

自己找到解决方案：问题在于使用'from'作为SMail类中的数据成员，并将'read'作为MailboxMessages类中的数据成员，因为它们是使用mysql的保留关键字。现在我的所有表都是创建的，更不用说复合键了。（通过数据库确认）

复合键的Hibernate解决方案

2 个答案: