Originally Posted by SoulkeepHL
As the title states, are there any Android apps that can directly read the Calibre database files? Not via OPDS or any other intermediary, just the db itself. I've poked around a fair bit, both here and on the greater interwebs, and my method of library management must be fairly uncommon, as I can't find any answers, or anyone else asking the same question. The closest I've seen is that Calibre Companion says it can manage your device library, but I wasn't sure if that meant it could read a Calibre library stored on a device, or if it just created its own library on a device.
Calibre companion integrates with calibre to copy parts (or all) of a calibre library to the device. It makes a copy of the metadata for the transferred books and updates that copy on every connect as a wireless device. From what you say, this isn't what you want.
You could try Leger Calibre (an Android app). It claims to read a calibre DB. I don't know if it works or what it actually does. Reading its description, you must copy the calibre database to the device. The app author specifically says that it won't work on a network share or cloud storage. For me, copying the library is worse than managing a subset of books, but it may be what you want to do.