What clears the lock created by select_for_update in Django?

Question

If I do a select_for_update, when/how does that lock get released? Some example code:

for rec_id in list(1,2,3):
    record = MyModel.objects.select_for_update().get(pk=rec_id)
    # Do several things to this record
    record.save()

Is the lock freed after the save() or is it freed after the view returns and the entire transaction is complete? How can I control the granularity of the lock?

The docs don't seem to say: https://docs.djangoproject.com/en/1.6/ref/models/querysets/#select-for-update

Answer 1

The lock is active for the duration of the transaction, which is controlled by you. So you control the granularity of the lock by controlling the granularity of the transaction, using the usual methods: @transaction.atomic, with transaction.atomic(), ATOMIC_REQUESTS = True, etc. See the transaction documentation.