获取ArrayField Postgres Django的len

Question

I've a model:-

class ModelA(models.Model):
    field1 = ArrayField(models.IntegerField())

I want to get the top10 objects of ModelA having maximum length of field1. I see that a len filter is available in Django Docs , but that just does not serves my purpose.

How can I get top10 objects having maximum length of field1?

Answer 1

If you are sure your array is 1-dimensional, you can use PostgreSQL function cardinality

ModelA.objects.extra(select={'length':'cardinality(field1)'}).order_by('length')

Or, using array_length function (with second argument being the number of dimensions sought)

ModelA.objects.extra(select={'length':'array_length(field1,1)'}).order_by('length')

Answer 2

I was finally able to get the frequency of the elements in the array as well:-

q = """
with norm (id, element) as (
    select id, unnest(field1) from model;
)
select id, sum(case when element = 2 then 1 else 0 end)  as count
from norm
group by id
order by count
limit 10;
"""


a = Model.objects.raw(q)