Django group by add non existing choices - django

Question

I have a model field that contains choices:
db_redirection_choices = (('A', 'first'), ('B', 'second'))
redirection_type = models.CharField(max_length=256, choices=db_redirection_choices, blank=True, null=True)
At some point I'm performing a group by on that column, counting all existing choices:
results = stats.values('redirection_type').annotate(amount=Count('redirection_type')).order_by('redirection_type')
However, this will give me only results for existings choices. I'd like to add the ones that are not even present with 0 to the results
e.g. If the table contains only the entry
Id | redirection_type
--------------------------
1 | 'A'
then the annotate will return only
'A': 1
of course that's normal, but I'd still like to get all non-existing choices in the results:
{'A': 1, 'B': 0}
What's the easiest way of accomplishing this?

Answer 1

I don't think there is an easy way to do it with the ORM, except maybe using a conditional expression, but that would make your query a lot more complicated, I think.
Why not do a simple post-processing in Python?
db_redirection_choices = (('A', 'first'), ('B', 'second'))
# I think your queryset will have a similar shape
results = [{'redirection_type': 'A', 'amount': 1}]
results_map = {
**{choice: 0 for choice, _display in db_redirection_choices},
**{res['redirection_type']: res['amount'] for res in results}
}
assert results_map == {'A': 1, 'B': 0}
If you don't need further processing in the ORM, that seems like the easiest.