On 7 Sep 2009, at 16:35 , Rob B (uk) wrote:
> Oh that just makes my brain hurt lol
It's not very hard to represent if you just use a few schemas:
This is the range of the promotion:
A B
|------------------|
And these are the possible research ranges relative to the promotion
(actual
values aren’t relevant):
a b
|----------|
a b
|--------------------------|
a b
|--------------|
a b
|------------|
a b
|--------|
a b
|------------|
Of these, only the last two won't "match" the promotion. What's the
difference
between the last two ranges and the previous 4? Well in the second-to-
last,
b < A, and in the last a > B. That's pretty much all.
So the matching condition is that we don't want either b < A or a > B:
`not (b < A or a > B)` ≡ `(not b < A) and (not a > B)` ≡ `b >
A and a < B`
Since we're performing the search on the promotion, we want the
promotion's data
first so we revert both operation and get `A < b and B > a`.
A and B are the start and end dates of promotion, and a and b are the
start and
end dates of our search, so in Python terms we need a promotion matching
`start_date < search.end_date and end_date > promotion.start_date`
which in Django filter terms becomes
`start_date__lt=search.end_date, end_date__gt=search.start_date`
And there you are.
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Django users" group.
To post to this group, send email to django-users@googlegroups.com
To unsubscribe from this group, send email to
django-users+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en
-~----------~----~----~----~------~----~------~--~---
