On Feb 24, 8:08 am, Timothy Kinney <timothyjkin...@gmail.com> wrote:
> I have models which describe a game. There are 61 provinces with 9
> rooms in each province, for a total of 549 locations. There are
> several hundred samurai, each assigned to a particular room id.
>
> Province(name, id, exits)
> Room(id, name, foreignkey('Province'))
> Samurai(id, name, foreignkey('Room'))
>
> I want to display a list of samurai (by id) for each province on the
> admin/change_list.html.
>
> I created a method in the Province model:
>
> def samurai(self):
> r = self.room_set.filter(province = self.pk).all()
> output = []
> for i in r:
> output.extend(i.samurai())
> return unicode(output)
>
> I use list_detail.object_list as the generic view and call the
> province.samurai method from my template:
>
> {% for province in object_list %}
> <tr>
> <td>{{ province.name }} [{{ province.id }}] </td>
> <td>{{ province.exits }}</td>
> <td>{{ province.samurai }} </td>
> </tr>
> {% endfor %}
>
> This is very slow, taking almost 4 seconds for 260 samurai.
>
> I know that the reason this is slow is because I am hitting the
> database so inefficiently. I have a for loop where each province is
> iterating 9 times and I am iterating this loop 61times.
>
> I'm new to databases and to django, so I'm trying to understand how I
> can grab all the data in one query and then just use it. I think I
> should do this from the view?
>
> Can you give me a list of steps (in pseudo-code) for optimizing this
> query?
>
> eg:
> 1) Get all objects in province from the view
> 2) create a dictionary
> 3) and so on...
>
> I just don't grok how the template, view, model method, and ORM fit
> together to make an efficient query. :/
>
> -Tim
You've identified the problem correctly, and the solution is fairly
complicated because it's a three-level relationship.
Without wanting to pimp my own blog, I've written quite a bit about
patterns of query optimisation which might help you to see the sort of
thing you need to do. See for example
http://blog.roseman.org.uk/2010/jan/11/django-patterns-part-2-efficient-reverse-lookups/
--
DR.
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