While HQL supports scalar functions (see user guide 15.27) the envers query API does not support them.

I suggest to change the signature of the method AuditProperty.function(String) to return an AuditProperty instead of an AuditProjection. Since AuditProperty implements AuditProjection this would not break existing code. However this change will break binary compatibility, is this a problem?

Code example:

AuditReader reader = ...;
reader.createQuery()
  .forEntitiesAtRevision(EntityA.class, 3)
  .add(AuditEntity.property("number")
  .function("STR").eqProperty("string"))