How do I add an annotation with Django annotate on a QuerySet?

Question

I have a model class with a status field, which might have several alternatives, say:

class MyModel(models.Model):
    status_choices = (
        ('status1', 'status1'),
        ('status2', 'status2'),
        ('status3', 'status3'),
        ('status4', 'status4'),
    )
    status = models.CharField(choices=status_choices)

Then I want to annotate the instances with an active field which might be either True or False. The instance is active when status is IN [status1, status2].

Django version is 1.11.

willeM_ Van Onsem · Accepted Answer · 2018-09-12 12:55:53Z

2

We can do this with a Case expression [Django-doc]:

from django.db.models import BooleanField, Case, Value, When

MyModel.objects.annotate(
    active=Case(
        When(status__in=['status1', 'status2'], then=Value(True))
        default=Value(False),
        output_field=BooleanField()
    )
)

Note that the list of the status__in condition should contain the keys of the choices (so the left item of the tuples, not the right one).

answered Sep 12, 2018 at 12:55

willeM_ Van Onsem

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