Comparing values from multiple tables; *show new posts* forum feature

[Piotr Husiatyński]

Hello,
I'm writing forum and I have a problem with *show new posts* feature.
Here's the code of my application:

http://github.com/husio/arch-pl/tree/09234f6d780c76b45b5e1a6576d80080507873d4/forum

I have two tables for *new* posts
- AllVisited for marking all posts as visited
- VisitedThread for remembering each post that user has seen

Line ~70 of view.py file is the incomplete question

dt = search_date_limit
unreaded = Thread.objects.filter(
Q(latest_post_date__gt=dt),
Q(visitedthread__isnull=True) |
Q(visitedthread__isnull=False,
visitedthread__date__lt= ? ) #
thread__latest_post_date ?
).distinct()[offset:offset + number]

The only thing I don't know how to do is how to check each
Thread.latest_post_date value during sql select and compare it with
VisitedThread.date value. How to write it?

[Malcolm Tredinnick]

Wait a few days until ticket #7210 is resolved and you'll be able to use
references to other fields as rhs values in filters. The work for that
is nearly complete, so it's pretty close to being committed. I'm fairly
sure that will help you there.

Regards,
Malcolm

[Piotr Husiatyński]

On 18 Sty, 12:06, Malcolm Tredinnick <malc...@pointy-stick.com> wrote:
> Wait a few days until ticket #7210 is resolved and you'll be able to use
> references to other fields as rhs values in filters. The work for that
> is nearly complete, so it's pretty close to being committed. I'm fairly
> sure that will help you there.

You mean #7210 http://code.djangoproject.com/ticket/7210 : "Added
expression support for QuerySet.update"
How that could solve my problem?

[Russell Keith-Magee]

#7210 gives you the ability to reference a field as the 'value' part
of a filter clause. So in your case, you could do something like:

Thread.objects.filter(latest_post_date__gt=F('visted_date")

to get all the objects where the latest post is after the visited date.

Yours
Russ Magee %-)