`delete()` after `difference()` in Django ORM

user_11251373 0
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Question is regarding delete() after difference() in Django ORM.

My goal here is to delete old model instances when amount of record in db greater then certain number.

class StatusLog(models.Model):
    logger_name = models.CharField(max_length=100)
    level = models.PositiveSmallIntegerField(choices=LOG_LEVELS, default=logging.ERROR, db_index=True)
    msg = models.TextField()
    trace = models.TextField(blank=True, null=True)
    create_datetime = models.DateTimeField(auto_now_add=True, verbose_name='Created at')

Plan:

  1. construct queryset with all entries.
  2. construct queryset with entries to keep.
  3. calculate difference
  4. delete rest.

Reality:

a = StatusLog.objects.all().order_by('pk')
a.count() = 93
# as planed

b = StatusLog.objects.all().order_by('pk')[:50]
b.count() = 50
# as planed

c = a.difference(b)
c.count() = 43
# as planed

c.update(trace='test') 
# returns 93. Updated whole table.
# WTF?????? Should be 43

Is it a bug or I don’t understand something?

django-orm django
1 Answers
StatusLog.objects.filter(id__in=list(StatusLog.objects.values_list('pk', flat=True)[:N])).delete()

Works like charm

user_68716760
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