Django ORM - Dynamically add When to Case

Question

I have a list of lists

my_list= [
    [1,2,3],
    [4,5,6],
    ...
]

I'd like to annotate some values like this:

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

MyModel.objects.filter(...).annotate(label=Case(When(some_value__in=my_list[0] then=Value('first list')), output_field=CharField()))

Now I need add a similar When for the other lists in my_list, but my_list could have different lengths.

How could I do this?

Answer 1

A Case expression can contain any number of Whens. You can create a list of When expressions and then unpack it into a Case:

whens = [When(some_value__in=l, then=Value('list #{}'.format(i)))\
            for i, l in enumerate(my_list)]

MyModel.objects.filter(...).annotate(label=Case(*whens, output_field=CharField()))