Michael, Thanks for your reply.
On Apr 1, 11:46 am, "Michael Bayer" <[email protected]> wrote: > there's a nested set demo in the examples/ folder of the distribution, > which uses MapperExtension as well as a little-used flag on the mapper > called "batch=False". are you building off of that ? No, I had wrote my own solution b/c I wanted to be able to support having multiple trees in the same table, but the solution in the example looked a little cleaner, so I switched to it. > as far as > multithread/process, the UPDATE statements which nested sets requires > would result in a lock of most of the table, thus protecting it from > concurrent updates. Yes, but I don't think that solves the problem. The problem isn't concurrent updates. The problem is that the update itself is built on stale data. Take code from the example: http://paste.pocoo.org/show/110684/ Note my comments. It seems to me that it is possible, although unlikely, that your entire tree structure will get corrupted unless you can assure that no other tree update process works between the the connection.scalar() and connection.execute(). Otherwise, if the tree is updated between those two calls, in a way that the affects the value returned from connection.scalar(), then the node structure in the table gets "corrupt". > nested sets is extremely inefficient in a > concurrent write environment. Agreed. The environment probably won't be that concurrent that I am concerned about efficiency. What I am concerned about is trying to prevent the node structure from getting corrupted. If there is even a remote possibility of the node structure getting corrupt, I would like to prevent it. > just that operator alone may render nested sets largely > obsolete. I will be happy when there is some kind of backend agnostic way to accomplish hierarchies. I can guarantee I won't miss nested sets. Thank you. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~----------~----~----~----~------~----~------~--~---
