I want to have versions from the same data entry. In other words, I want to duplicate the entry with another version number.
id - Version will be the primary key.
How should the entity look like? How can I duplicate it with another version?
id Version ColumnA 1 0 Some data 1 1 Some Other data 2 0 Data 2. Entry 2 1 Data You can make an Embedded class, which contains your two keys, and then have a reference to that class as EmbeddedId in your Entity.
You would need the @EmbeddedId and @Embeddable annotations.
@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; } 
@Generatedvalue for Id's by EmbeddedId
@GeneratedValue can only be used to generate key values for a primary key, it cannot generate combination for composite keys.Section - 11.1.17 GeneratedValue Annotation of JPA 2.0 Specification. It clearly says that, @GeneratedValue can only be used with simple primary key.
The MyKey class must implement Serializable if you are using @IdClass
Key class:
@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.
AUTOGENERATED. oder something like that @GeneratedValue(strategy = GenerationType.IDENTITY)
hash and prime in method hashCode in class EntryKey, can you tell me where that idea comes from?The MyKey class (@Embeddable) should not have any relationships like @ManyToOne
@IdClassannotation, another tip I found is the@Columnannotation should go into the Entity class' fields (YourEntityin RohitJan's sample code).