On Wed, 2008-09-17 at 19:30 -0500, Chris Stromberger wrote:
> Disclaimer: Django newbie here.
>
> I have a join type of model access in one of my views like so:
>
> recent_staff_reviews =
> StaffReview.objects.order_by('-last_update').filter(enabled =
> True).filter(restaurant__enabled = True)[:4]
>
> where the StaffReview model has a foreign key to the Restaurant model.
> So this produces a join query behind the scenes to get to the enabled
> field on the restaurants table (I have seen the queries via a
> "djangosnippet" I installed to show the behind-the-scene queries).
> But the join query produced only grabs fields from the review table.
> In the template, I access various parts of the Restaurant model via
> the review list (so using the foreign key), like
>
> {% for review in recent_staff_reviews %}
> ...
> review.restaurant.name ...etc
>
> Doing this results in a new query on the restaurant table for each
> restaurant referenced in the review list. But...the original query
> already did the join and could have returned these restaurant fields
> all in the one query.
It could have, but it's more expensive by default (doing joins can often
be done with indexes and doesn't need to necessarily read the table
data).
What you're looking for is the select_related() Queryset method.
Regards,
Malcolm
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