What's the cleanest way of counting the iteration of a queryset loop?-CodePudding

I need to loop through a queryset and put the objects into a dictionary along with the sequence number, i, in which they appear in the queryset. However a Python for loop doesn't seem to provide a sequence number. Therefore I've had to create my own variable i and increment it with each loop. I've done something similar to this, is this the cleanest solution?

ledgers = Ledger.objects.all()
i = 0

for ledger in ledgers:
    print('Ledger no ' str(i) ' is ' ledger.name)
    i  = 1

CodePudding user response：

enumerate(…) [Python-doc] is designed for that:

ledgers = Ledger.objects.all()

for i, ledger in enumerate(ledgers):
    print(f'Ledger no {i} is {ledger.name}')

CodePudding user response：

You can annotate the index like that:

from django.db.models import Window, F

ledgers = Ledger.objects.annotate(index=Window(expression=DenseRank(), order_by=F('id').desc()))

ledgers_dict = dict(ledgers.values_list('index', 'name'))

ledgers.filter(index__lt=5, name__contains='foo')  # ledgers is a queryset

With that you get a queryset that you can use for further database operations.

DenseRank