API to get item name from item id

src/calibre/db/cache.py

@@ -388,6 +388,10 @@ class Cache(object):
                 return self.fields[field].table.book_col_map.copy()
             raise ValueError('%s is not a many-one or many-many field' % field)
 
+    @read_api
+    def get_item_name(self, field, item_id):
+        return self.fields[field].table.id_map[item_id]
+
     @read_api
     def author_data(self, author_ids=None):
         '''

src/calibre/db/legacy.py

@@ -90,6 +90,13 @@ class LibraryDatabase(object):
                 return func
             setattr(self, 'get_%s_with_ids' % field,
                     MT(getter(field)))
+        for field in ('author', 'tag', 'series'):
+            def getter(field):
+                field = field if field == 'series' else (field+'s')
+                def func(self, item_id):
+                    return self.new_api.get_item_name(field, item_id)
+                return func
+            setattr(self, '%s_name' % field, MT(getter(field)))
 
         # Legacy field API
         for func in (

src/calibre/db/tests/legacy.py

@@ -32,7 +32,9 @@ class ET(object):
         return newres
 
 def compare_argspecs(old, new, attr):
-    ok = len(old.args) == len(new.args) and len(old.defaults or ()) == len(new.defaults or ()) and old.args[-len(old.defaults or ()):] == new.args[-len(new.defaults or ()):]  # noqa
+    num = len(old.defaults or ())
+
+    ok = len(old.args) == len(new.args) and old.defaults == new.defaults and (num == 0 or old.args[-num:] == new.args[-num:])
     if not ok:
         raise AssertionError('The argspec for %s does not match. %r != %r' % (attr, old, new))
 
@@ -165,6 +167,9 @@ class LegacyTest(BaseTest):
             '!get_publishers_with_ids':[()],
             '!get_ratings_with_ids':[()],
             '!get_languages_with_ids':[()],
+            'tag_name':[(3,)],
+            'author_name':[(3,)],
+            'series_name':[(3,)],
         }.iteritems():
             for a in args:
                 fmt = lambda x: x