如何在JPA中創建和處理復合主鍵

Question

我想擁有來自相同數據條目的版本。 換句話說，我想用另一個版本號復制該條目。

id - Version將是主鍵。

該實體應該如何？ 如何與其他版本復制？

id Version ColumnA

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

Answer 1

您可以創建一個包含兩個鍵的Embedded class ，然后在您的Entity引用該類作為EmbeddedId 。

您需要@EmbeddedId和@Embeddable注釋。

@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 **/
}

---

實現此任務的另一種方法是使用@IdClass注釋，並將您的id放在該IdClass 。 現在，您可以在兩個屬性上使用普通的@Id注釋

@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

如果您使用@IdClass ，MyKey類必須實現Serializable

Answer 3

關鍵課程：

@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;
}

實體類：

@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;
    ...
}

如何與其他版本復制？

您可以分離從提供程序檢索的實體，更改Entry的鍵，然后將其作為新實體保留。

Answer 4

MyKey類（@Embeddable）不應該有像@ManyToOne這樣的任何關系