[chaley]

LibraryDatabase2 is obsolete. It works with the new database introduced in V4 because Kovid supplied a "legacy" replacement.

For all new code it is best to use something like this:

def init_cache(library_path):
   from calibre.db.backend import DB
   from calibre.db.cache import Cache
   backend = DB(library_path)  # other named parameters as needed
   cache = Cache(backend)
   cache.init()
   return cache

Use the methods in Cache.

For older code that uses methods in LibraryDatabase2, use something like this:

from calibre.db.legacy import LibraryDatabase
db = LibraryDatabase(library_path) # other named parameters as needed

In this case the methods in "Cache" are available via db.new_api.

I think the new_api attribute might be available in LibraryDatabase2 through some sort of monkeypatching, but I am not sure of that.