A brief description of the easy-to-err error in SQLAlchemy sorting

This article mainly describes the python in the sqlalchemy sort of a pit, the text gives a detailed sample code, the need for friends can reference, interested friends to learn from the following together.

Objective

SQLAlchemy is an ORM framework in the Python programming language that builds on database APIs and uses relational object mappings for database operations, in short: converting objects to SQL and then executing SQL using the data API and getting execution results. Recently in the use of sqlalchemy sort encountered a pit, so want to summarize down, share to more friends, below to see together.

The Code of the Pit

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. All ()

No pits of code

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 ()). All ()  query = query.filter (Uservideo.status = = 1)  query = query.order_by (UserVideo.vid.desc ())  query = Query.limit (). All ()

Yes, you're right, that's the horizontal bar, slow speed. Change desc() to function speed can be increased by 10 times times

Attached below is a sqlalchemy high-performance random fetching of several strips of data

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 = Queryquery_tail = Query_tail.join (Rvid, Uservideo.vid > Rvid.c.rvid). Limit (+). All ()

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