I'm building a complex ETL tool with SQLAlchemy that will sometimes need to let the user "preview" a changed record - not actually carry out the update, just find out which fields would be changed, and to what values. I'm having trouble figuring out a good way to do it.
Is there a way to get a sort of preview of an update - get information about what updates are pending for the next flush, or get a flush to report back its changes without actually performing it? One approach would be to set echo to True, let the user see the echo, then roll back the transaction, but there are a couple reasons I don't think that will work for me. I don't want to make the user mentally parse SQL statements; I'd like to get a dict of the pending changes and write my own code to display them attractively, instead. Anyway, I'm having trouble getting echo to work on this app. (The whole thing is part of a TurboGears project, and my echoes aren't showing up, probably because of something I don't understand about the SQLAlchemy logging configuration.) Just getting to the bind variables that will ultimately be sent along with the UPDATE statement would be a great solution, and I'm trying to figure out where I could get them. Right now, it looks like the `params` dict is assembled in Mapper._save_obj in orm/mapper.py, used at line 1376 to issue connection.execute, then discarded. I'm considering overriding Mapper with my own version whose __save_obj can exit at this point, returning `params`, if it is invoked with a "preview=True" parameter... but that seems a little scary. __save_obj is a long method, and I'd have to keep my app's version of it carefully synched with the canonical sqlalchemy version indefinitely. Thanks in advance for reading through, and for any any suggestions! -- - Catherine http://catherinedevlin.blogspot.com/ *** PyOhio * July 25-26, 2009 * pyohio.org *** --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
