how to annotate each object with random value

Question

I want to have items with random annotations.

I tried this:

items = Item.objects.all().annotate(random_value=Value(randint(1,6)),output_field=PositiveIntegerField()))

And it is random, but THE SAME for EVERY Item in QuerySet.

But I want to have DIFFERENT value for EACH Item...

Any ideas?

You here evaluate `randint`, for example to `5`, and then you annotate each item with that `5`. — Willem Van Onsem, Mar 27 '21 at 16:50
As of Django-3.2, `Random` will be available: https://docs.djangoproject.com/en/dev/ref/models/database-functions/#random — Willem Van Onsem, Mar 27 '21 at 16:52
no, but it requires some work to define a `Random` expression manually, etc, especially since for the different SQL "dialects", these are different expressions: https://github.com/django/django/blob/main/django/db/models/functions/math.py#L144-L158. — Willem Van Onsem, Mar 27 '21 at 16:58

score 1 · Accepted Answer · answered Mar 28 '21 at 13:00

According @Willem Van Onsem suggestion it is possible in Django<3.2:

def my_view(request):
    from django.db.models.expressions import Func
    from django.db.models.functions.mixins import (
        FixDecimalInputMixin, NumericOutputFieldMixin,
    )
    class Random(NumericOutputFieldMixin, Func):
       function = 'RANDOM'
       arity = 0

       def as_mysql(self, compiler, connection, **extra_context):
           return super().as_sql(compiler, connection, function='RAND', **extra_context)

       def as_oracle(self, compiler, connection, **extra_context):
           return super().as_sql(compiler, connection, function='DBMS_RANDOM.VALUE', **extra_context)

       def as_sqlite(self, compiler, connection, **extra_context):
           return super().as_sql(compiler, connection, function='RAND', **extra_context)

       def get_group_by_cols(self, alias=None):
           return []


    items = Item.objects.all().annotate(random_value=Round(Random()*5+1))

I did it inside def my_view, because if 3.2 becomes stable I remove this and add global from django.models.db import Round

how to annotate each object with random value

1 Answers1