I’m already doing all of that. The problem is we often have logic that goes
like:
model = Product.get_subtable(‘foo’)
queryset = model.objects.
filter(…).
select_related(…).
exclude(…).
extra(…)
… and so on and so on. Seriously, the method that constructs the queryset
is some 1500 lines long and can quite a bit to run
if queryset.count() == 0:
model = Product.get_subtable(‘bar’)
queryset = model.objects.
filter(…).
select_related(…).
exclude(…).
extra(…)
… the same expensive method again.
A lot of our performance gains have come from caching the queryset creation
function, but even with all of that the method can still take 200ms to run.
(Seriously, there can be over 40 filters, some of which are complex Q() and F()
objects.) The problem is the second queryset produces almost the exact same
SQL, but with one table having a different name. Back when we were creating the
raw SQL, it was a simple string replace to switch tables. I was hoping that
someone had some kind of “switch table” command on the queryset or something
similar.
> On Mar 17, 2015, at 3:08 AM, James Schneider <jrschneide...@gmail.com> wrote:
>
> That sounds more like an exact use case for model inheritance. You would
> define a single model that matches the columns in both tables. You can define
> that model as abstract, then have the two real models (one for each table)
> inherit from that abstract model. In the definition for the child models, you
> would specify the DB table names to match your two tables in the existing
> schema.
>
> https://docs.djangoproject.com/en/1.7/ref/models/options/#db-table
> <https://docs.djangoproject.com/en/1.7/ref/models/options/#db-table>
> That way, you only maintain a single (abstract) model definition, even though
> multiple models use it (each with a separate DB table).
>
> You may also need to mark the real models as unmanaged by the ORM if you're
> doing funny things directly in the DB, and you will be managing the table
> schema directly for those tables.
>
> https://docs.djangoproject.com/en/1.7/ref/models/options/#managed
> <https://docs.djangoproject.com/en/1.7/ref/models/options/#managed>
> I'm assuming you have already determined the logic deciding which model each
> user uses. At that point, assuming that all other functionality remains the
> same (calls/processing the data, regardless of table), the calls to those
> models can be generalized by a simple utility function that returns a class
> instance of the necessary model.
>
> def get_right_model(user):
> # logic to pick ModelA or ModelB based on user
> return ModelA
>
> Then later, maybe in a view:
>
> selected_model = get_right_model(self.request.user)
>
> all_data = selected_model.objects.all()
>
> #all_data should now contain the results of the query against the right
> model/table in the DB
>
> Trying to flip between tables in the ORM by tweaking the innards probably is
> going to lead to excessive complication.
>
> -James
>
> --
> You received this message because you are subscribed to the Google Groups
> "Django users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to django-users+unsubscr...@googlegroups.com
> <mailto:django-users+unsubscr...@googlegroups.com>.
> To post to this group, send email to django-users@googlegroups.com
> <mailto:django-users@googlegroups.com>.
> Visit this group at http://groups.google.com/group/django-users
> <http://groups.google.com/group/django-users>.
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/django-users/CA%2Be%2BciXKkQ2Lpq1F-KBpHkndLWxi_8dCVamXJ-G7Bji3QZWcmA%40mail.gmail.com
>
> <https://groups.google.com/d/msgid/django-users/CA%2Be%2BciXKkQ2Lpq1F-KBpHkndLWxi_8dCVamXJ-G7Bji3QZWcmA%40mail.gmail.com?utm_medium=email&utm_source=footer>.
> For more options, visit https://groups.google.com/d/optout
> <https://groups.google.com/d/optout>.
Peter of the Norse
rahmc...@radio1190.org
--
You received this message because you are subscribed to the Google Groups
"Django users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to django-users+unsubscr...@googlegroups.com.
To post to this group, send email to django-users@googlegroups.com.
Visit this group at http://groups.google.com/group/django-users.
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-users/0435A65C-4A7A-4DFA-A1C2-8951437FFB2B%40Radio1190.org.
For more options, visit https://groups.google.com/d/optout.
