基于现有字段的Django查询集更新

Question

I need to update Django queryset bookings_to_save in such a way:

for booking in bookings_to_save:
    booking.status = Booking.STATUS_CHOICES.approved
    booking.title = 'ST{}{}'.format(booking.pk, booking.created.strftime('%Y%m%d'))
    booking.save()

I tried something like this:

bookings_to_save.update(
    status=Booking.STATUS_CHOICES.approved,
    title='ST{}{}'.format(F('id'), F('created'))
)

In SQL I would do like this:

update bookings_booking bb set title='ST' || bb.id || to_char(bb.created, 'YYYYMMDD') where << some condition >>;

Is there any way how can I accomplish this task using django tools?

Answer 1

According to https://docs.djangoproject.com/en/1.7/ref/models/queries/#supported-operations-with-f that does not seem to be supported yet. Ideally it would look like:

bookings_to_save.update(
    status=Booking.STATUS_CHOICES.approved,
    title='ST' + F('id') + F('created'))
)

because the operations supported are operators on F (the F s need to be part of the outer expression to form an F-expression).

One could also imagine a new kind of string expression (S-expressions; sorry Lisp readers):

bookings_to_save.update(
    status=Booking.STATUS_CHOICES.approved,
    title=S('ST{}{}', F('id'), F('created')))
)