With the Envers query system has been extended with the ability to traverse associations for *-to-one assocations. However, this is limited to inner-joins. With HHH-16, HQL has been extended to support joins on unrelated entities, which enables support for left joins in audit queries.
The already existing Envers query API should be improved, such that left-joins are supported when traversing associations, too. The inner join implementation should also leverage the new unrelated entity join mechanism.
Furthermore, the Envers query API should be extended such that criterias on properties from two related entities can be expressed together in a conjunction, disjunction and in a direct property relation expression.