如何在JPA中创build和处理复合主键

我想要从相同的数据input版本。 换句话说，我想复制与另一个版本号的条目。 id – 版本将是主键。

实体应该如何？

我怎样才能复制与另一个版本？

id Version ColumnA 1 0 Some data 1 1 Some Other data 2 0 Data 2. Entry 2 1 Data 

Answer 1

您可以创build一个包含您的两个键的Embedded class ，然后在您的Entity中将该类引用为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 **/ } 

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另一种实现这个任务的方法是使用@IdClass注释，并将你的id放在IdClass 。 现在你可以在这两个属性上使用普通的@Id注解

 @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

如果使用@IdClass则MyKey类必须实现Serializable

Answer 3

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; } 

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; ... } 

我怎样才能复制与另一个版本？

您可以分离从提供程序中检索的实体，更改Entry的键，然后将其作为新的实体保留。

Answer 4

MyKey类（@Embeddable）不应该像@ManyToOne那样有任何关系