如何在 JPA 中创建和处理复合主键

我希望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条目。

id - Version将是主键。

实体应该是什么样子的? 我如何复制它与另一个版本？

id Version ColumnA


1   0      Some data
1   1      Some Other data
2   0      Data 2. Entry
2   1      Data
205854 次浏览
小开
最佳答案

您可以创建一个包含两个键的 Embedded class，然后在 Entity中将对该类的引用作为 EmbeddedId。

您将需要 @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 **/
}

Another way to achieve this task is to use @IdClass annotation, and place both your id in that IdClass. Now you can use normal @Id annotation on both the attributes

@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;
}
小开

主要类别:

@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;
}

Entity class:

@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;
...
}

How can I duplicate it with another Version?

You can detach entity which retrieved from provider, change the key of Entry and then persist it as a new entity.

小开

The MyKey class must implement Serializable if you are using @IdClass

小开

MyKey 类(@Embeddable)不应该具有像@ManyToOne 这样的关系


提交答案