[EMAIL PROTECTED] wrote:
> I have searched through the dev list and couldn't find anything
> relating to the specific thing I am trying to do. I also am aware that
> both QuerySet and OneToOne fields are in some sort of flux right now.
>
> QuerySet is being completely refactored, and I will of course wait for
> that (like my admin changes) to drop before trying to come up with a
> patch. OneToOne field has also been pending changes for about forever
> now and I don't know exactly what's going on with it. So this post is
> to start a dialog about whether we can follow OneToOne relationships
> in a bi-directional manner and what the current plans are.
I like this idea a lot, it's definitely something that's been a
hindrance on things I'm working on. OneToOneFields are special, they
seem like they should provide the relationship whichever way I need to
(since by its very nature, all this stuff could have just been in one
table, so I'm just isolating groups of data that are still single
row-centric into multiple tables). Use this example:
class Account(models.Model):
username = models.CharField(maxlength=20)
password = models.CharField(maxlength=20)
active = models.BooleanField()
class AccountPersonInfo(models.Model):
account = OneToOneField(Account)
first_name = models.CharField(maxlength=20)
last_name = models.CharField(maxlength=20)
class AccountCompanyInfo(models.Model):
account = OneToOneField(Account)
company_name = models.CharField(maxlength=20)
company_address = models.CharField(maxlength=20)
Now, there's no possible *.objects.select_related() I can use that will
get me the information in all three of these tables.
* Account.objects.select_related() - Only gives me Account, not
AccountPersonInfo or AccountCompanyInfo
* AccountPersonInfo.objects.select_related() - Only gives me Account and
AccountPersonInfo, not AccountCompanyInfo
* AccountCompanyInfo.objects.select_related() - Only gives me Account
and AccountCompanyInfo, not AccountPersonInfo
I can get any two, but not all three. If I want the third, it requires
a second hit to the database. If I'm selecting one record, that's not
so bad. But when I do this:
Account.objects.select_related().filter(active=True)
If I want the information in AccountPersonInfo *and* AccountCompanyInfo
for the N (for argument, say hundreds of) records it returns, it will do
that N rows worth of queries for the other table. This is a performance
destroyer.
So, my alternatives are:
1) Run 2-3 queries, pulling the linked records back, and then merging
them on the Python side. UGLY.
2) Just use a hand-coded query. Also UGLY, since the Models have
methods on them that I'd like to use, and populating them by hand from
the results of the QuerySet is more than a minor annoyance.
3) Make OneToOneFields bidirectional.
For obvious reasons, I think (3) is the right choice. Is there anything
that would prevent QuerySet or the Models from working this way?
Thanks,
George
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