Django Aggregate Max 没有为 CharField 提供正确的最大值

Question

I have this query to give me the next available key from the DB. It works just fine until it get to 10, where it will say that 10 is available when it's not

max_var = ShortUrl.objects.filter(is_custom=False).aggregate(max=Cast(Coalesce(Max('key'), 0),BigIntegerField()))['max'] + 1

The column is a CharField.

Any tips on how to fix this?

Answer 1

You need to annotate (cast string to int) first. Then you can find the aggregate of casted value. ie:

from django.db.models import BigIntegerField
from django.db.models.functions import Cast
from django.db.models import Max

max_var = ShortUrl.objects.filter(is_custom=False) \
    .annotate(key_int = Cast('key', output_field=BigIntegerField())) \
    .aggregate(max=Max('key_int'))['max'] or 0

max_var+=1