Add a single row to the list of cached database-rows.

This avoids additional queries to init a single object afterwards. On high-performance systems or large object-nets, this could reduce the amount of database-queries fired drastically. For best performance, include the matching row of the tables system, system_date and system_rights. Use the class-filter if you want to make sure the cached row matches a single target-class. This makes sense if you query tables of an inheritance-structure (and not all tables may be in the cache-row resultset).