#Django import
from django.db import transaction
from django.db.models import Min, Max
#Proyect imports
from core.models import Cert


def test_for_update():

        #We retrieve certs to work with them
        certs = Cert.objects.all().order_by('pk')
        certs = certs.select_for_update()# Thats the magic!
        total_rows = certs.count()
        print('{0} rows in total'.format(total_rows))

        #get batch size
        batch_size = int(input('Define Batch Size: '))

        print('It should need {0} selects to finish.'.format(total_rows/batch_size))

        with transaction.atomic():
            full = True
            while full:
                #Select for update
                batch = certs[batch_size]
                #We collect data to show:
                data = batch.aggregate(Min('pk'), Max('pk'))
                batch_count = batch.count()
                #We print
                print('{0} to {1} with {2} rows...'.format(
                    data['pk__min'],
                    data['pk__max'],
                    batch_count
                ))
                #condition to exit:
                if batch_count < batch_size:
                    full = False

            print('Finished process, success!')