[Django]-Django ORM how to Round an Avg result

Use Func() expressions.

Here’s an example using the Book model from Django Aggregation topic guide to round to two decimal places in SQLite:

class Round(Func):
    function = 'ROUND'
    template='%(function)s(%(expressions)s, 2)'

Book.objects.all().aggregate(Round(Avg('price')))

This allows the round function to be parameterised (from @RichardZschech’s answer):

class Round(Func):
  function = 'ROUND'
  arity = 2

Book.objects.all().aggregate(Round(Avg('price'), 2))

Building on previous answers, I’ve come to this solution to make it work for PostgreSQL:

from django.db.models import Func

class Round2(Func):
    function = "ROUND"
    template = "%(function)s(%(expressions)s::numeric, 2)"

# Then use it as ,e.g.:
# queryset.annotate(ag_roi=Round2("roi"))

# qs.aggregate(ag_sold_pct=Round2(Sum("sold_uts") / (1.0 * Sum("total_uts"))) * 100

Improving on @mrts answer.

This allows the round function to be parameterised:

class Round(Func):
  function = 'ROUND'
  arity = 2

Book.objects.all().aggregate(Round(Avg('price'), 2))

Django has the Round function. For more detail please see the documentation

I needed to have both PostgreSQL and SQLite support, but also keep the ability to specify the number of digit to keep.

Build on previous answers :

class Round(Func):
    function = 'ROUND'
    arity = 2
    # Only works as the arity is 2
    arg_joiner = '::numeric, '

    def as_sqlite(self, compiler, connection, **extra_context):
        return super().as_sqlite(compiler, connection, arg_joiner=", ", **extra_context)

# Then one can use it as:
# queryset.annotate(avg_val=Round(AVG("val"), 6))

I would have prefered something cleaner like

if SQLITE:
    arg_joiner=", "
elif PGSQL:
    arg_joiner = '::numeric, '
else raise NotImplemented()

but did not find how, feel free to improve !