Sorry Kovid, I fail to understand You.
I *am* using calibredb with a remote server ("calibredb <command> --library-path=http://syno0:38081/#lib --username=<mself> --password=<secret>")
... but I'm also calling it multiple times: for each book I do:
1) calibredb search (to get id if book exists)
2) calibredb add --empty --title=<Title> --authors=<Authors> --isbn=<ISBN> (if book did not exist)
3) calibredb set_metadata <id> --field=identifiers:isbn:<ISBN>,dewey:<Dewey> --field=#collecton --field=publisher:<publisher> ...
4) calibredb set_metadata <id> --field=cover:<coverImage>
5) calibredb add_format <id> --don't-replace <content file>
I could possibly collapse (3 and 4) and (2 and 5) but it still leaves me with 3 calibredb calls for each book.
As said I also tried preparing a local directory structure (one book per directory) and use "calibredb -1 -r", but that completely ignores the "metadata.opf" file and, since most of content files do not have metadata, even title is mostly bogus.
What should I do, exactly?