[kbenson]

I've fallen head over heels for (Perl's) DBIx::Class and it's ability to "prefetch" joined data[1]. In short, it will populate the top level objects, as well as the items they join to from a single query (yes the DB will have to send duplicate info). I find it really convenient.

Recently I've wondered what other ORMs support this feature or something similar to it. Anyone care to comment?

[1] https://metacpan.org/module/DBIx::Class::ResultSet#prefetch

[damagednoob]

It sounds like what you're referring to is something I know as eager loading[1]. Most good ORMS have this e.g. Django[2], NHibernate[3], Rails[4]. The 'select N+1' problem[5] is fairly common.

[1] http://stackoverflow.com/questions/1299374/what-is-eager-loa...

[2] https://docs.djangoproject.com/en/dev/ref/models/querysets/#...

[3] http://nhforge.org/blogs/nhibernate/archive/2008/09/06/eager...

[4] http://guides.rubyonrails.org/active_record_querying.html#ea...

[5] http://stackoverflow.com/questions/97197/what-is-the-n1-sele...

[kbenson]

Ah, that's probably a much easier term to google. Part of the problem always seems to boil down to terminology. :) I figured it must be present in other ORMs, it seemed way to useful to not be pervasive.

It looks like select_related is the equivalent Django method to what I'm referring to in DBIx::Class, although prefetch_related (which you linked) looks superior in many respects. I'm fairly certain DBIx::Class allows a similar method to prefetch_related, but it may or may not be automatically done. I know it supports object caching, so it shouldn't be to hard to achieve in a few lines (but automatic is nice).

Interestingly, I don't see a way in Django to specify complex select fields to be included along with the default fields for a record. In a simple case that can be used to get a count of something, in complex cases it could be used to actually compute something on the DB to group and/or limit by (group by having). I'm probably just not familiar enough with QuerySets from this small bit of exposure to work it out.

NHibernate... That's a lot of code for something that should be simple. I imagine that's for explanatory reasons, and that much code isn't needed for most queries.