Question

I am trying to add an additional custom field to a django model. I have been having quite a hard time figuring out how to do the following, and I will be awarding a 150pt bounty for the first fully correct answer when it becomes available (after it is available — see as a reference Improving Python/django view code).

I have the following model, with a custom def that returns a video count for each user —

class UserProfile(models.Model):
    user = models.ForeignKey(User, unique=True)
    positions = models.ManyToManyField('Position', through ='PositionTimestamp', blank=True)

    def count(self):
        from django.db import connection
        cursor = connection.cursor()
        cursor.execute(
        """SELECT (
            SELECT COUNT(*)
                FROM videos_video v
                WHERE v.uploaded_by_id = p.id
                OR EXISTS (
                    SELECT NULL
                    FROM videos_videocredit c
                    WHERE c.video_id = v.id
                    AND c.profile_id = p.id
                )
            ) AS Total_credits
            FROM userprofile_userprofile p
            WHERE p.id = %d"""%(int(self.pk))
        )
        return int(cursor.fetchone()[0])

I want to be able to order by the count, i.e., UserProfile.objects.order_by('count'). Of course, I can’t do that, which is why I’m asking this question.

Previously, I tried adding a custom model Manager, but the problem with that was I also need to be able to filter by various criteria of the UserProfile model: Specifically, I need to be able to do: UserProfile.objects.filter(positions=x).order_by('count'). In addition, I need to stay in the ORM (cannot have a raw sql output) and I do not want to put the filtering logic into the SQL, because there are various filters, and would require several statements.

How exactly would I do this? Thank you.

Answer 1

“couldn’t you use something like the “extra” queryset modifier?”

see the docs

I didn’t put this in an answer at first because I wasn’t sure it would actually work or if it was what you needed – it was more like a nudge in the (hopefully) right direction.

in the docs on that page there is an example

query

Blog.objects.extra(
    select={
        'entry_count': 'SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id'
    },
)

resulting sql

SELECT blog_blog.*, (SELECT COUNT(*) FROM blog_entry WHERE blog_entry.blog_id = blog_blog.id) AS entry_count
FROM blog_blog;

Perhaps doing something like that and accessing the user id which you currently have as p.id as appname_userprofile.id

note:

Im just winging it so try to play around a bit.
perhaps use the shell to output the query as sql and see what you are getting.