all_formats()

src/calibre/db/cache.py

@@ -363,6 +363,9 @@ class Cache(object):
     @read_api
     def all_field_names(self, field):
         ''' Frozen set of all fields names (should only be used for many-one and many-many fields) '''
+        if field == 'formats':
+            return frozenset(self.fields[field].table.col_book_map)
+
         try:
             return frozenset(self.fields[field].table.id_map.itervalues())
         except AttributeError:

src/calibre/db/legacy.py

@@ -68,6 +68,7 @@ class LibraryDatabase(object):
         for field in ('authors', 'tags', 'publisher', 'series'):
             name = field[:-1] if field in {'authors', 'tags'} else field
             setattr(self, 'all_%s_names' % name, partial(self.new_api.all_field_names, field))
+        self.all_formats = partial(self.new_api.all_field_names, 'formats')
 
         for func, field in {'all_authors':'authors', 'all_titles':'title', 'all_tags2':'tags', 'all_series':'series', 'all_publishers':'publisher'}.iteritems():
             setattr(self, func, partial(self.field_id_map, field))

src/calibre/db/tests/legacy.py

@@ -158,6 +158,7 @@ class LegacyTest(BaseTest):
             'custom_field_keys':[(True,), (False,)],
             'get_usage_count_by_id':[('authors',), ('tags',), ('series',), ('publisher',), ('#tags',), ('languages',)],
             'get_field':[(1, 'title'), (2, 'tags'), (0, 'rating'), (1, 'authors'), (2, 'series'), (1, '#tags')],
+            'all_formats':[()],
         }.iteritems():
             for a in args:
                 fmt = lambda x: x