To audit changes that are performed on an entity, you only need two things: the hibernate-envers jar on the classpath and an @Audited annotation on the entity.

And that's all - you can create, modify and delete the entities as always. If you look at the generated schema for your entities, or at the data persisted by Hibernate, you will notice that there are no changes. However, for each audited entity, a new table is introduced - entity_table_AUD, which stores the historical data, whenever you commit a transaction. Envers automatically creates audit tables if hibernate.hbm2ddl.auto option is set to create, create-drop or update. Otherwise, to export complete database schema programatically, use org.hibernate.envers.tools.hbm2ddl.EnversSchemaGenerator. Appropriate DDL statements can be also generated with Ant task described later in this manual.

Instead of annotating the whole class and auditing all properties, you can annotate only some persistent properties with @Audited. This will cause only these properties to be audited.

The audit (history) of an entity can be accessed using the AuditReader interface, which can be obtained having an open EntityManager or Session via the AuditReaderFactory. See the javadocs for these classes for details on the functionality offered.

It is possible to configure various aspects of Hibernate Envers behavior, such as table names, etc.

The name of the audit table can be set on a per-entity basis, using the @AuditTable annotation. It may be tedious to add this annotation to every audited entity, so if possible, it's better to use a prefix/suffix.

If you have a mapping with secondary tables, audit tables for them will be generated in the same way (by adding the prefix and suffix). If you wish to overwrite this behaviour, you can use the @SecondaryAuditTable and @SecondaryAuditTables annotations.

If you'd like to override auditing behaviour of some fields/properties inherited from @Mappedsuperclass or in an embedded component, you can apply the @AuditOverride(s) annotation on the subtype or usage site of the component.

After the basic configuration it is important to choose the audit strategy that will be used to persist and retrieve audit information. There is a trade-off between the performance of persisting and the performance of querying the audit information. Currently there two audit strategies.

When Envers starts a new revision, it creates a new revision entity which stores information about the revision. By default, that includes just

Envers handles this information as an entity. By default it uses its own internal class to act as the entity, mapped to the REVINFO table. You can, however, supply your own approach to collecting this information which might be useful to capture additional details such as who made a change or the ip address from which the request came. There are 2 things you need to make this work.

@Entity
@RevisionEntity( MyCustomRevisionListener.class )
public class MyCustomRevisionEntity {
    ...
}

public class MyCustomRevisionListener implements RevisionListener {
    public void newRevision(Object revisionEntity) {
        ( (MyCustomRevisionEntity) revisionEntity )...;
    }
}

An alternative method to using the org.hibernate.envers.RevisionListener is to instead call the getCurrentRevision method of the org.hibernate.envers.AuditReader interface to obtain the current revision, and fill it with desired information. The method accepts a persist parameter indicating whether the revision entity should be persisted prior to returning from this method. true ensures that the returned entity has access to its identifier value (revision number), but the revision entity will be persisted regardless of whether there are any audited entities changed. false means that the revision number will be null, but the revision entity will be persisted only if some audited entities have changed.

You can think of historic data as having two dimension. The first - horizontal - is the state of the database at a given revision. Thus, you can query for entities as they were at revision N. The second - vertical - are the revisions, at which entities changed. Hence, you can query for revisions, in which a given entity changed.

The queries in Envers are similar to Hibernate Criteria queries, so if you are common with them, using Envers queries will be much easier.

The main limitation of the current queries implementation is that you cannot traverse relations. You can only specify constraints on the ids of the related entities, and only on the "owning" side of the relation. This however will be changed in future releases.

Please note, that queries on the audited data will be in many cases much slower than corresponding queries on "live" data, as they involve correlated subselects.

Envers persists audit data in reaction to various Hibernate events (e.g. post update, post insert, and so on), using a series of even listeners from the org.hibernate.envers.event.spi package. By default, if the Envers jar is in the classpath, the event listeners are auto-registered with Hibernate.

Conditional auditing can be implemented by overriding some of the Envers event listeners. To use customized Envers event listeners, the following steps are needed:

For each audited entity (that is, for each entity containing at least one audited field), an audit table is created. By default, the audit table's name is created by adding a "_AUD" suffix to the original table name, but this can be overridden by specifying a different suffix/prefix in the configuration or per-entity using the @org.hibernate.envers.AuditTable annotation.

The primary key of the audit table is the combination of the original id of the entity and the revision number - there can be at most one historic entry for a given entity instance at a given revision.

The current entity data is stored in the original table and in the audit table. This is a duplication of data, however as this solution makes the query system much more powerful, and as memory is cheap, hopefully this won't be a major drawback for the users. A row in the audit table with entity id ID, revision N and data D means: entity with id ID has data D from revision N upwards. Hence, if we want to find an entity at revision M, we have to search for a row in the audit table, which has the revision number smaller or equal to M, but as large as possible. If no such row is found, or a row with a "deleted" marker is found, it means that the entity didn't exist at that revision.

The "revision type" field can currently have three values: 0, 1, 2, which means ADD, MOD and DEL, respectively. A row with a revision of type DEL will only contain the id of the entity and no data (all fields NULL), as it only serves as a marker saying "this entity was deleted at that revision".

If you'd like to generate the database schema file with the Hibernate Tools Ant task, you'll probably notice that the generated file doesn't contain definitions of audit tables. To generate also the audit tables, you simply need to use org.hibernate.tool.ant.EnversHibernateToolTask instead of the usual org.hibernate.tool.ant.HibernateToolTask. The former class extends the latter, and only adds generation of the version entities. So you can use the task just as you used to.

For example:

<target name="schemaexport" depends="build-demo"
  description="Exports a generated schema to DB and file">
  <taskdef name="hibernatetool"
    classname="org.hibernate.tool.ant.EnversHibernateToolTask"
    classpathref="build.demo.classpath"/>

  <hibernatetool destdir=".">
    <classpath>
      <fileset refid="lib.hibernate" />
      <path location="${build.demo.dir}" />
      <path location="${build.main.dir}" />
    </classpath>
    <jpaconfiguration persistenceunit="ConsolePU" />
    <hbm2ddl
      drop="false"
      create="true"
      export="false"
      outputfilename="versioning-ddl.sql"
      delimiter=";"
      format="true"/>
  </hibernatetool>
</target>

Will generate the following schema:

    create table Address (
        id integer generated by default as identity (start with 1),
        flatNumber integer,
        houseNumber integer,
        streetName varchar(255),
        primary key (id)
    );

    create table Address_AUD (
        id integer not null,
        REV integer not null,
        flatNumber integer,
        houseNumber integer,
        streetName varchar(255),
        REVTYPE tinyint,
        primary key (id, REV)
    );

    create table Person (
        id integer generated by default as identity (start with 1),
        name varchar(255),
        surname varchar(255),
        address_id integer,
        primary key (id)
    );

    create table Person_AUD (
        id integer not null,
        REV integer not null,
        name varchar(255),
        surname varchar(255),
        REVTYPE tinyint,
        address_id integer,
        primary key (id, REV)
    );

    create table REVINFO (
        REV integer generated by default as identity (start with 1),
        REVTSTMP bigint,
        primary key (REV)
    );

    alter table Person
        add constraint FK8E488775E4C3EA63
        foreign key (address_id)
        references Address;