前言
SQLAlchemy是Python编程语言下的一款ORM框架,该框架建立在数据库API之上,使用关系对象映射进行数据库操作,简言之便是:将对象转换成SQL,然后使用数据API执行SQL并获取执行结果。最近在使用SQLAlchemy排序遇到了一个坑,所以想着总结下来,分享给更多的朋友,下面来一起看看吧。
坑的代码
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query = db_session.query(UserVideo.vid,
UserVideo.uid,
UserVideo.v_width,
UserVideo.v_height,
UserVideo.create_time,
UserVideo.cover,
UserVideo.source_url,
UserVideo.v_type,
UserVideo.category,
User.username,
User.sex,
UserExtraInfo.avatar,
UserExtraInfo.watermark)
query = query. filter (UserVideo.status = = 1 ,
User.uid = = UserVideo.uid,
UserExtraInfo.uid = = UserVideo.uid)
query = query. filter (UserVideo.status = = 1 )
query = query.order_by( - UserVideo.vid)
query = query.limit( 20 ). all ()
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不坑的代码
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query = db_session.query(UserVideo.vid,
UserVideo.uid,
UserVideo.v_width,
UserVideo.v_height,
UserVideo.create_time,
UserVideo.cover,
UserVideo.source_url,
UserVideo.v_type,
UserVideo.category,
User.username,
User.sex,
UserExtraInfo.avatar,
UserExtraInfo.watermark)
query = query. filter (UserVideo.status = = 1 ,
User.uid = = UserVideo.uid,
UserExtraInfo.uid = = UserVideo.uid) # .order_by(UserVideo.vid.desc()).limit(20).all()
query = query. filter (UserVideo.status = = 1 )
query = query.order_by(UserVideo.vid.desc())
query = query.limit( 20 ). all ()
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对,你没看错,就是那个横杠,拉慢速度。改成 desc()
函数速度能提高10倍
下面附上一个 sqlalchemy 高性能随机取出若干条数据
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query = db_session.query(UserVideo.vid,
UserVideo.uid,
UserVideo.v_width,
UserVideo.v_height,
UserVideo.create_time,
UserVideo.cover,
UserVideo.source_url,
UserVideo.v_type,
UserVideo.category,
User.username,
User.sex,
UserExtraInfo.avatar,
UserExtraInfo.watermark)
query = query. filter (UserVideo.status = = 1 , User.uid = = UserVideo.uid, UserExtraInfo.uid = = UserVideo.uid)
rvid = db_session.query(func. round (random.random() * func. max (UserVideo.vid)).label( 'rvid' )).subquery()
query = query. filter (UserVideo.category = = category)
query_tail = query
query_tail = query_tail.join(rvid, UserVideo.vid > rvid.c.rvid).limit( 20 ). all ()
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总结
以上就是这篇文章的全部内容了,希望本文的内容对大家的学习或者工作能带来一定的帮助,如果有疑问大家可以留言交流,谢谢大家对服务器之家的支持。