Django annotate count with a distinct field

Question

I have two models defined loosely like this:

class InformationUnit(models.Model):
    username = models.CharField(max_length=255)
    project = models.Foreig         


        

Answer 1

Count can take a distinct argument, like so:

p = Project.objects.all().annotate(Count('informationunit__username', 
                                         distinct=True))

This doesn't seem to be documented, but you can find it in the source for Count.

Answer 2

SQL SELECT field1, COUNT(DISTINCT(pk)) FROM project GROUP BY field1 ORDER BY NULL;

QuerySet

Project.objects.all().values(field1).annotate(count=Count('pk', distinct=True)).order_by()

Answer 3

If you just want to count the distinct values, you can use the distinct() and count() functions:

count = Project.objects.values('informationunit__username').distinct().count()

Answer 4

Project.objects.all().annotate(Count('informationunit__username', 
                                     distinct=True))