Question

I have been lurking and learning in here for a while. Now i have a problem that somehow i cannot see an easy solution. In order to learn django i am bulding an app that basically keeps track of booked items.
What I would like to do is to show how many days per month for a selected year one item has been booked.

i have the following models:

Asset(Model)

BookedAsset(Model):
 asset = models.ForeignKey(Asset)
 startdate = models.DateField()
 enddate = models.DateField()

So having the following entries:

asset 1, 2010-02-11, 2010-02-13
asset 2, 2010-03-12, 2010-03-14
asset 1, 2010-04-30, 2010-05-01

I would like to get returned the following:

asset 1    asset 2
-------    -------
Jan = 0    Jan = 0
Feb = 2    Feb = 0
Mar = 0    Mar = 2
Apr = 1    Apr = 0
May = 1    May = 0
Jun = 0    Jun = 0
Jul = 0    Jul = 0
Aug = 0    Aug = 0
Sep = 0    Sep = 0
Oct = 0    Oct = 0
Nov = 0    Nov = 0
Dec = 0    Dec = 0

I know i need to first get the number of days in a date range (and keep track if they fall out of the current month and into the next month) and then do an agregate on the number of days. I am just stuck on how to do it elegantly in Django.

Any help (or hint in the right direction) is greatly appreciated.

Answer 1

At the end I went with a custom query as a solution to my question:

cursor = connection.cursor()
cursor.execute("""select to_char(allmonths.yeardate::date, 'YYYY/MM/DD') as monthdate,
                    COUNT("day") as bookings
                    from (
                    select distinct date_trunc('month', (date %s - offs)) as yeardate 
                    from generate_series(0,365,28) as offs
                    ) as allmonths
                    left join bookings_bookedassetday 
                    on EXTRACT(MONTH from "day")=EXTRACT(MONTH from yeardate) 
                    and asset_id=%s and EXTRACT(YEAR from "day") = %s
                    group by allmonths.yeardate
                    order by allmonths.yeardate asc""", [year+'-12-31', id, year])

query = cursor.fetchall()

Maybe it is not the most django-ist way of doing it but I found it way easier than figuring it out with pure django 😐

If somebody else has a better alternative I am all ears 🙂