I just updated to the latest digikam on fedora 27. It tries to do a database migration on startup, which fails. I assumed this was because I was using a mysql server.
I raised a bug this morning, and have already had an update and a fix, which is to change dbconfig.xml to the one in the bug report below.
This worked for me. Looking at the date on the rpm it was built just before this file was updated upstream, so hopefully the next release will have it included.
Regards,
Chris