...

src/calibre/db/backend.py

@@ -25,7 +25,8 @@ from calibre.utils.config import to_json, from_json, prefs, tweaks
 from calibre.utils.date import utcfromtimestamp, parse_date
 from calibre.utils.filenames import is_case_sensitive
 from calibre.db.tables import (OneToOneTable, ManyToOneTable, ManyToManyTable,
-        SizeTable, FormatsTable, AuthorsTable, IdentifiersTable, CompositeTable)
+        SizeTable, FormatsTable, AuthorsTable, IdentifiersTable,
+        CompositeTable, LanguagesTable)
 # }}}
 
 '''
@@ -604,11 +605,12 @@ class DB(object):
         for col in ('series', 'publisher', 'rating'):
             tables[col] = ManyToOneTable(col, self.field_metadata[col].copy())
 
-        for col in ('authors', 'tags', 'formats', 'identifiers'):
+        for col in ('authors', 'tags', 'formats', 'identifiers', 'languages'):
             cls = {
                     'authors':AuthorsTable,
                     'formats':FormatsTable,
                     'identifiers':IdentifiersTable,
+                    'languages':LanguagesTable,
                   }.get(col, ManyToManyTable)
             tables[col] = cls(col, self.field_metadata[col].copy())
 

src/calibre/db/cache.py

@@ -13,7 +13,8 @@ from functools import wraps, partial
 
 from calibre.db.locking import create_locks, RecordLock
 from calibre.db.fields import create_field
-from calibre.ebooks.book.base import Metadata
+from calibre.db.tables import VirtualTable
+from calibre.ebooks.metadata.book.base import Metadata
 from calibre.utils.date import now
 
 def api(f):
@@ -189,7 +190,8 @@ class Cache(object):
                 if table.metadata['datatype'] == 'composite':
                     self.composites.add(field)
 
-            self.fields['ondevice'] = create_field('ondevice', None)
+            self.fields['ondevice'] = create_field('ondevice',
+                    VirtualTable('ondevice'))
 
     @read_api
     def field_for(self, name, book_id, default_value=None):

src/calibre/db/tables.py

@@ -13,6 +13,7 @@ from dateutil.tz import tzoffset
 
 from calibre.constants import plugins
 from calibre.utils.date import parse_date, local_tz, UNDEFINED_DATE
+from calibre.utils.localization import lang_map
 from calibre.ebooks.metadata import author_to_author_sort
 
 _c_speedup = plugins['speedup'][0]
@@ -54,6 +55,19 @@ class Table(object):
         self.link_table = (link_table if link_table else
                 'books_%s_link'%self.metadata['table'])
 
+class VirtualTable(Table):
+
+    '''
+    A dummy table used for fields that only exist in memory like ondevice
+    '''
+
+    def __init__(self, name, table_type=ONE_ONE, datatype='text'):
+        metadata = {'datatype':datatype, 'table':name}
+        self.table_type = table_type
+        Table.__init__(self, name, metadata)
+
+
+
 class OneToOneTable(Table):
 
     '''
@@ -210,3 +224,9 @@ class IdentifiersTable(ManyToManyTable):
         for key in tuple(self.col_book_map.iterkeys()):
             self.col_book_map[key] = tuple(self.col_book_map[key])
 
+class LanguagesTable(ManyToManyTable):
+
+    def read_id_maps(self, db):
+        ManyToManyTable.read_id_maps(self, db)
+        lm = lang_map()
+        self.lang_name_map = {x:lm.get(x, x) for x in self.id_map.itervalues()}