On May 29, 3:48 am, motard <stun...@gmail.com> wrote:
> Hi!
>
> Thanks for all your suggestions. I've been able to solve the issue.
> Now the page reports to be executing roughly 80-90 SQL queries and is
> performing well.
>
> The problem was mainly in two places of my code where I was looping
> through all the results of a related set for every row in a paged
> object. The problem hasn't become evident earlier because being an
> intranet application, the site does not receive much traffic.
>
> Once the related set has started to grow, the problem has emerged.
>
> I was doing something like this:
>
> {% for element in mypagedlist.object_list %}
> {% for related_element in element.related_element_set.all %}
> #Do something
> {% endfor %}
> {% endfor %}
I would write something like the following in your view:
#1:get a list of outer loop IDs
id_list=OuterLoopObject.objects.filter(criteria).values_list
('id',flat=True)
#2:get a mapping of ID to actual object
outer_dict=OuterLoopObject.objects.values().in_bulk(id_list)
#3:get a list of all inner loop objects whose FK points to an outer
loop object
inner_object_list=InnerLoopObject.filter
(outerobject__id__in=id_list).values()
#4:put a n empty list in every outer_dict object
for o in outer_dict.values():
o['innerlist']=[]
#5: loop through the list of inner objects; use the stored ID in the
inner object as a key for the outer_dict
for item in inner_object_list:
outer_object=outer_dict[item['outerobject_id']]
outer_object['innerlist'].append(item)
#6: get a list of outer_dict's values()
outer_list=outer_dict.values()
#7: send to template
return render_to_response(template_name, {'outer_list':outer_list})\
Advantages:
*Three queries total rather than one per outer object
*No Python objects are created , so there's far less overhead there
Disadvantages:
Kind of more memory use
*As it is now you can't do anything in the template but access
attributed of inner_list. There are ways around that but they're all
annoying. It's possible to do what I wrote using actual objects and
select_related, but then you get way more overhead and way more memory
use.
I have a lot of views that do things similar to yours, and this is the
best way I have found to handle it.
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