On Aug 19, 9:25 pm, "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote:
> Daniel,
>
> Thank you for your reply.
>
> Following your advice I tried the following:
>
> task is the model that relates to project.
>
> <ul>
> {% for task in project.task.all %}
> <li>{{ task.title }}</li>
> {% endfor %}
> </ul>
>
> It doesn't show anything so I think I'm confusing my models. Am I
> missing something obvious ? I am only writing this project management
> app to try and learn django ^^
>
> One last question, if django automatically joins tables on foreign
> keys doesn't that make most queries quite expensive in terms of
> performance ?
>
> Thanks again
The for loop should be
{% for task in project.task_set.all %}
- the _set suffix is added automatically. See the db-api documentation
for more on this.
This functionality doesn't make queries expensive generally. The SQL
query getting the tasks won't happen until you actually iterate
through the set of objects (task_set, in this case). So this view
would actually generate two queries: one to get the original object,
and another one to get the joined objects.
If you create your own views rather than using the built-in generic
ones - which you'll need to do once you start doing anything
complicated - you specify your queryset operations directly, and
therefore get some control over the SQL, via things like
select_related(). (Although this wouldn't help in this case, as it
doesn't work on 'reverse' foreign key relationships like the one we're
talking about here.)
If you're interested in the actual SQL produced, go into the shell and
do
from django.db import connection
then try a few queryset operations, and then type
connection.queries
to see a list of the SQL statements that have been executed. Or, to
see it on your site, install the DebugFooterMiddleware from here:
http://www.djangosnippets.org/snippets/766/ - you'll get a little
button on your page which will expend into a list of the all the SQL
executed in producing the view.
--
DR.
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