On Wed, Dec 16, 2009 at 7:56 PM, Jeremy Dunck <[email protected]> wrote:
> On Dec 15, 2009, at 11:16 PM, "Sean O'Connor"
> <[email protected]> wrote:
>
>> In regard to the deferred fields option, I'll let Jacob speak for
>> his view but I've approached such functionality as "nice to have"
>> for the patch since its not critical to the patch being useful.
>> Personally I haven't had the time to figure it out and implement it
>> so my original patch didn't include it.
>
> I like the idea of the deferred fields, but if we don't implement it
> now, people may come to rely on the AttributeError so that we can't
> add deferred later. Perhaps a note in the docs stating our intent to
> add deferreds would suffice?
No need for workaround docs - I've just uploaded an RC3 patch that
implements deferred fields.
The one gotcha on this patch is that it now requires that you request
the primary key when you retrieve an object. That is, you can't just
run::
Author.objects.raw('SELECT firstname, lastname FROM author')
You must now include the pk:
Author.objects.raw('SELECT id, firstname, lastname FROM author')
If you don't, you get an exception. Unfortunately, it's an exception
after the SQL has been executed, but that's the only way to know
exactly which columns have been requested.
This is slightly more restrictive than Jacob's RC2 patch - but I think
the RC3 behaviour is preferable. The primary key value is a fairly
essential part of the Django infrastructure. In RC2, if you retrieved
an Author with firstname and lastname, then saved the object, you
would get a new object in the database. RC3 avoids this because the
deferred object has the right primary key.
If the price of avoiding surprises like this is forcing the PK to be
retrieved, I think it's a price worth paying. If you really can't
afford to have the PK retrieved, then I'd argue you aren't retrieving
a Django object; you can still call on raw SQL cursors to accommodate
those use cases.
Yours,
Russ Magee %-)
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