Django - aggregation with get_FOO_display

Question

Consider the following:

status = queryset.values('status').annotate(count=Count('status'))

where status field is a CharField with choices. This will result in a list of dictionaries with status DB value along with its count.

Is there a way to aggregate status and show its display value instead? I have looked up the code of _get_FIELD_display which I probably can emulate, but it feels a tad hackish to repeat the framework's internal code.

Sphinx

Can you update your question with a input -> expected output example? – Margay

@Margay isn't the question clear enough? status -> status aggregated with its display value – Sphinx

My bad, I missed that status has choices. – Margay

Answer 1

Without hacking a SQL, you may not achieve this in DB level easily. But, since get_FOO_display operates on Model level, you don't even have to hack _get_FIELD_display or lookup in choices manually (If the following method does not cost your server too much):

YourModel(status=status).get_status_display()

Thus

for s in queryset.values('status').annotate(count=Count('status')):
    print(queryset.model(status=s['status']).get_status_display())

Paella

get_FOO_display is added dynamically, it's not available like you put it, unless you meant something else. Can you provide a working example? – Sphinx

Thanks, exactly what I wanted. – Sphinx

Answer 2

Take a look at django.contrib.admin.util.display_for_field function. You have to find the field object:

field = queryset.model._meta.get_field('status')
        

Then you can use it as:

display_for_field(status, field)

Or, in your case:

{ unicode(display_for_field(t['status'], field)): t['count']
    for t in queryset.values('taxonomy').annotate(count=models.Count('taxonomy'))}

Necessarian

What is taxonomy indicating here? Why doesn't status belong in the values args, given that it is the column he is trying to group by? I'm interested in accomplishing this without an extra for loop. – Ire

it seems that display_for_field does exists in django >3 on this library. – Keever

Answer 3

On Django >2, I usually transform the annotated dataset on a list of dict and then apply this function:

dataset =list(MyModel.objects.all().values('status').annotate(count=Count('id')))
dataset = transform_display(dataset,MyModel,'status')

def transform_display(dataset, model_class, field_name):
    for item in dataset:
        field_value = item[field_name]
        instance = model_class(**{field_name: field_value})
        display_method = getattr(instance, f"get_{field_name}_display", None)
        new_value = display_method()
        if new_value:
            item[field_name] = new_value
    return dataset

Keever