如何使用SQLAlchemy ORM实现子选择?

我有以下型号:

• 相册:id,name,…
• 曲目:ID,专辑ID,…

我需要使用sqlacalchemy orm生成下面的查询:

SELECT 
  Album.name,
  (
    SELECT COUNT(*) as total_count
    FROM Track
    WHERE Track.album_id = Album.id
  ) as tracks
FROM
  Album
WHERE
  Album.band = ‘Metallica’ AND
  tracks.total_count > 10

迄今为止的准则是:

tracks = session \
  .query(func.count('*').label('total_count')) \
  .select_from(Track) \
  .filter(Track.album_id == Album.id) \
  .subquery()

query = session \
  .query(Album.name, tracks.c.total_count) \
  .filter(Album.band == 'Metallica') \
  .filter(tracks.c.total_count > 10)

生成的查询如下:

SELECT
  Album.name,
  anon_1.total_count
FROM
  Album,
  (
    SELECT count('*') AS total_count
    FROM Track, Album
    WHERE Track.album_id = Album.id
  ) AS anon_1
WHERE
  Album.band = ‘Metallica’ AND
  anon_1.total_count > 10

这要慢得多。有什么想法我如何返回作为根选择一部分的子选择结果?谢谢!