test if instance in queryset django

1. Use the exists() method to check if an instance exists in a queryset.
2. The exists() method returns True if the queryset contains any results, and False if the queryset is empty.
3. This method is more efficient than calling len() on the queryset or converting it to a list to check for existence.
4. Example:

if queryset.exists():
    # Do something if the instance exists in the queryset
else:
    # Do something if the instance does not exist in the queryset