How to create and handle composite primary key in JPA

Question

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

User · Answer

The MyKey class must implement Serializable if you are using  IdClass

User · Answer

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

User · Answer

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   amp  amp  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

User · Answer

The MyKey class   Embeddable  should not have any relationships like  ManyToOne

[java] How to create and handle composite primary key in JPA

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