On Oct 3, 10:44 pm, Carl Meyer <c...@oddbird.net> wrote:
> Hi Luke,
>
> On Oct 3, 9:04 am, Luke Plant <l.plant...@cantab.net> wrote:
>
> > The patch for this is now ready, as far as I'm concerned, but I'd like
> > to bring it up here again before committing, mainly because Alex Gaynor
> > expressed some doubts.
>
> > The latest patch is on the ticket:
>
> >https://code.djangoproject.com/ticket/16937
>
> I know I'm a bit late to the party here (had a work deadline last
> Friday). I think this functionality is valuable and makes sense to
> have in the ORM, thanks for all the work on it. Though I don't have
> time to go through the patch in detail, it seems like its gotten
> several pairs of eyes over it closely already.
>
> My only real concern is one I'm a bit surprised hasn't been raised
> already: API and naming sanity. If I'm a new user coming to this API,
> as far as I'm concerned "select_related" and "prefetch_related" may as
> well be synonyms - they don't tell me anything useful about how the
> functions differ. And even knowing the internal details, any
> justification for the naming seems tortured at best: both methods use
> selects, and both prefetch something that would otherwise have to be
> fetched separately later.
One convincing reason for merging select_related and prefetch_related
is that if you have a setup like:
Author -> foreign key: favorite_book -> Book -> m2m: authors -> Author
If you do Author.objects.prefetch_related('favorite_book__authors')
without issuing .select_related you will currently run a query for
each author to fetch his favorite book. Then the authors would be
fetched in a single query using prefetch. This is of course not what
the user wants. If the above prefetch_related call results in
automatic select_related, it would be a good idea to have the method
called .select_related.
The only problem I can think of is that if you for some reason want to
clear prefetch_related but not select_related you can't do that. But
that is not too bad of a problem.
- Anssi
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