> -----Original Message----- > From: sqlalchemy@googlegroups.com [mailto:sqlalchemy@googlegroups.com] > On Behalf Of Michael Bayer > Sent: 27 September 2011 19:37 > To: sqlalchemy@googlegroups.com > Subject: Re: [sqlalchemy] Possible bug with subqueryload > > > On Sep 27, 2011, at 1:16 PM, King Simon-NFHD78 wrote: > > > > Great, thanks a lot :-) I only discovered it in a toy > application, and > the workaround (including order_by on the query) is not a > problem. > > In this toy application, I was also wondering if there existed > a > mechanism for doing some sort of "lazy subqueryload". ie. I'm > loading a > collection of objects and I don't know ahead of time if I'm > going to > access a particular relationship (so I don't want to eagerload > it). > However, if I *do* access it, I'm going to access it on each > object in > the collection, so I'd like to load all the related objects in > a single > hit. It's just like a subqueryload, except it is only executed > when the > relationship is accessed for the first time. > > Is that a silly idea? Or perhaps it already exists and I've > missed it. > > > > It actually exists in Hibernate, but not for us. We do sort of > have the infrastructure in place to make it possible, i.e.the > subqueryload right now prepares a Query object at query time that > fires off during load time, with a mapper option it would need to > stick it as some kind of memo in each InstanceState, it would be very > tricky to implement. Keeping that state and keeping it plugged > into the InstanceStates, then what if the loader was fired after many > of the other states have been garbage collected, just a lot of corner > cases to deal with. > > it can be handrolled of course, the general technique when you want > to construct objects such that they appear "loaded" is to use > attributes.set_commited_value() to set an attribute such that the ORM > sees it as "what was loaded from the database". an example of that > is where we first introduced the "subquery" concept here: > http://www.sqlalchemy.org/trac/wiki/UsageRecipes/DisjointEagerLoading >
Ah yes, set_committed_value is exactly the sort of thing I was looking for. Thanks a lot, Simon -- 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.
