[sqlalchemy] Re: What's the use of expunge?
On Feb 26, 2009, at 1:29 AM, 一首诗 wrote: The document says: Expunge removes an object from the Session, sending persistent instances to the detached state, and pending instances to the transient state: I hoped that if an instance was expunged from a session, I might use it safely as a container of some temp data without fearing trigger any database query. But I found that if an object is 'expunge'd , it's properties will not be accessible anymore. So, when should we use expunge? Or it is kept for sqlalchemy inner use only? you can reattach the object to a session later if you need it to be part of a transaction again.it can be used for caching scenarios, for example. But I agree most reasonable applications probably won't use expunge() very much. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: What's the use of expunge?
Previously Michael Bayer wrote: On Feb 26, 2009, at 8:21 AM, Wichert Akkerman wrote: What happens if you do not call expunge on it, but pickle the object in a cache, load it later and then merge it? the state of the newly unpickled object, that is the current value of its mapped attributes, would be merged with the persistent version in the session. merge() will load the object from the database into an in-session, persistent instance before merging the external state. because your unpickled instance never actually enters the session, conflicts with its previous session or an already present in-session object are nicely avoided. I actually skip that and invalidate the cache entry on changes to prevent that SQL hit. What I meant was: does it matter if you never explicitly call expunge? Wichert. -- Wichert Akkerman wich...@wiggy.netIt is simple to make things. http://www.wiggy.net/ It is hard to make things simple. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: What's the use of expunge?
On Feb 26, 2009, at 10:27 AM, Wichert Akkerman wrote: Previously Michael Bayer wrote: On Feb 26, 2009, at 8:21 AM, Wichert Akkerman wrote: What happens if you do not call expunge on it, but pickle the object in a cache, load it later and then merge it? the state of the newly unpickled object, that is the current value of its mapped attributes, would be merged with the persistent version in the session. merge() will load the object from the database into an in-session, persistent instance before merging the external state. because your unpickled instance never actually enters the session, conflicts with its previous session or an already present in-session object are nicely avoided. I actually skip that and invalidate the cache entry on changes to prevent that SQL hit. What I meant was: does it matter if you never explicitly call expunge? for pickling ? not at all. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
