如何在JPA中创建和处理复合主键

Question

我想拥有来自相同数据条目的版本.换句话说,我想用另一个版本号复制该条目.

id - Version 将是主键.

该实体应该如何？如何与其他版本复制？

id Version ColumnA

1   0      Some data
1   1      Some Other data
2   0      Data 2. Entry
2   1      Data

Answer 1

您可以创建一个Embedded class包含两个键的,然后EmbeddedId在您的类中引用该类Entity.

你需要@EmbeddedId和@Embeddable注释.

@Entity
public class YourEntity {
    @EmbeddedId
    private MyKey myKey;

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

    /** Your getters and setters **/
}

@Embeddable
public class MyKey implements Serializable {

    @Column(name = "Id", nullable = false)
    private int id;

    @Column(name = "Version", nullable = false)
    private int version;

    /** getters and setters **/
}

实现此任务的另一种方法是使用@IdClass注释,并将其id置于其中IdClass.现在,您可以@Id在两个属性上使用常规注释

@Entity
@IdClass(MyKey.class)
public class YourEntity {
   @Id
   private int id;
   @Id
   private int version;

}

public class MyKey implements Serializable {
   private int id;
   private int version;
}

Answer 2

Serializable如果您正在使用MyKey类必须实现@IdClass

Answer 3

关键类别：

@Embeddable
@Access (AccessType.FIELD)
public class EntryKey implements Serializable {

    public EntryKey() {
    }

    public EntryKey(final Long id, final Long version) {
        this.id = id;
        this.version = version;
    }

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

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

    public Long getVersion() {
        return this.version;
    }

    public void setVersion(Long version) {
        this.version = version;
    }

    public boolean equals(Object other) {
        if (this == other)
            return true;
        if (!(other instanceof EntryKey))
            return false;
        EntryKey castOther = (EntryKey) other;
        return id.equals(castOther.id) && version.equals(castOther.version);
    }

    public int hashCode() {
        final int prime = 31;
        int hash = 17;
        hash = hash * prime + this.id.hashCode();
        hash = hash * prime + this.version.hashCode();
        return hash;
    }

    @Column (name = "ID")
    private Long id;
    @Column (name = "VERSION")
    private Long operatorId;
}

实体类：

@Entity
@Table (name = "YOUR_TABLE_NAME")
public class Entry implements Serializable {

    @EmbeddedId
    public EntryKey getKey() {
        return this.key;
    }

    public void setKey(EntryKey id) {
        this.id = id;
    }

    ...

    private EntryKey key;
    ...
}

如何将其复制到另一个版本？

您可以分离从提供程序检索的实体，更改Entry的键，然后将其持久保存为新实体。