On 25 huhti, 23:44, Alex Ogier <alex.og...@gmail.com> wrote:
> On Thu, Apr 25, 2013 at 2:10 PM, Florian Apolloner
> <f.apollo...@gmail.com>wrote:
>
> > On Thursday, April 25, 2013 7:06:06 PM UTC+2, Adrian Holovaty wrote:
>
> >> Also, I should mention that this should be *optional* behavior, as the
> >> current behavior is reasonable for the common case. The API for specifying
> >> this "load everything" behavior is a separate discussion. Perhaps a keyword
> >> argument like: User.objects.only('username', loadall=True).
>
> > I could imagine a Meta attribute which introduces so called "deferred
> > groups" like SA has
> >http://docs.sqlalchemy.org/en/latest/orm/mapper_config.html#deferred-...,
> > accessing one column of a group will load all columns of the group. Not
> > sure if we want that level of control, but I thought it would be worth to
> > look what SA can do in this regard.
>
> I think groups are a very good abstraction for this problem. The two common
> cases are probably "Load this column alone, because it's potentially a big
> honking blob of text or binary" and "Load everything we don't have on this
> object, because we are actually using it actively". Groups let you solve
> both problems flexibly. The downside is that they might not be very DRY,
> having to repeat group="everything" over and over if you just want to load
> it all on first access.
+1 to this approach.
IMO load everything is a better default than one field at a time. When
deferred field loading happens something has already gone wrong. In
almost every case it is better to try to minimize the amount of
queries than the amount of loaded fields. The cases where you have
deferred multiple fields, need only one of them later on, and there is
a field that you can't load due to potentially huge value are
hopefully rare.
But, I don't really care too much. If the objects come from DB queries
instead of something like the use case of Adrian then if you end up
doing deferred field loading you have already failed. So, even an
error on deferred field access would work for my use cases of defer...
- Anssi
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