How can I optimize my database queries using my actual django model?

Question

I can't post image because I'm new so here's a link of what I want.

So, I have the model on the left and I want the view on the right.
As of now, I'm looping over every thread I'm interested in. Template code:

{% for thread in threadlist %}
{% for post in thread.postlist %}
...

Model code:

class Thread (models.Model):
...    
def postlist(self):
    posts = list(self.post_set.all())
    return [posts.pop(0)] + posts[-2:]

There must be a way to do this with less queries by joining columns or something. I'm pretty new to Python/Django and I don't really know how to do this.

Arthur Debert · Accepted Answer · 2009-08-24 13:21:33Z

2

You can use select_related . This will make the query follow joins so you end up with one larger query, instead of many smaller ones.

The docs are pretty thorough.

answered Aug 24, 2009 at 13:21

Arthur Debert

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MrHus · Accepted Answer · 2009-08-24 12:47:08Z

0

Looking at the documentation you should be using post_set.all(). I'm pretty sure that the queries are joined by django behind the scenes, and that its lazy. Meaning it won't be loaded until its needed.

From the documentation:

QuerySets are lazy -- the act of creating a QuerySet doesn't involve any database activity. You can stack filters together all day long, and Django won't actually run the query until the QuerySet is evaluated.

answered Aug 24, 2009 at 12:47

MrHus

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1 Comment

knarf Over a year ago

I'm doing a query for each thread, that's 10+ queries per page. I want only 1 loop instead of having 2 nested ones. "QuerySets are lazy" means they're only executed when necessary and here every one of them is. My actual solution is not optimal.

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