JPA : Versioning

JPA allows objects of classes to be versioned. The version is typically used as a way of detecting if the object has been updated by another thread or EntityManager since retrieval using the current EntityManager - for use by Optimistic Transactions.

Version Field/Property

JPAs mechanism for versioning of objects is to mark a field of the class to store the version. The field must be Integer/Long based. With JPA you can specify the details of this version field as follows.

<entity name="mydomain.User">
    <attributes>
        <id name="id"/>
        <version name="version"/>
    </attributes>
</entity>

or alternatively using annotations

@Entity
public class User
{
    @Id
    long id;

    @Version
    int version;

    ...
}

The specification above will use the "version" field for storing the version of the object. DataNucleus will use a "version-number" strategy for populating the value.

Surrogate Version for Class

While the above mechanism should always be used for portability, DataNucleus also supports a surrogate version for objects of a class. With this you don't have a particular field that stores the version and instead DataNucleus persists the version in the datastore with the field values in its own "column" You do this as follows.

import org.datanucleus.api.jpa.annotations.SurrogateVersion;

@Entity
@SurrogateVersion
public class User
{
    @Id
    long id;

    ...
}