Now that we have DBIx::Class, we should use it wherever possible.
Long term steps:
1) Replace all DBI inserts and deletes with DBIC creates and deletes
2) Replace all DBI selects with DBIC searches using DBIx::Class::ResultClass::HashRefInflator to return hashrefs for compatibility
3) Move logic from perl modules into Result and ResultSet classes wherever possible and sensible.
As we are using Koha::Object(s) now, this is not needed now.