[chaley]

Try something like this test program (which works):

from calibre.ebooks.metadata.book.base import Metadata
from calibre.library.database2 import LibraryDatabase2
from calibre.utils.config import prefs


class MyMetadata(Metadata):

    def __init__(self, mi):
        Metadata.__init__(self, None)
        self.smart_update(mi, replace_metadata=True)

    def mm_print(self, attr):
        print attr, '=', getattr(self, attr, 'not found')

src = prefs['library_path']
db = LibraryDatabase2(src)

my_mi = MyMetadata(db.get_metadata(1283, index_is_id=True))
print my_mi
my_mi.mm_print('application_id')