save() in a loop. (Data Migrations example).

I'm wondering about this code snippet from the documentation

for person in Person.objects.all():

    person.name = '%s %s' % (person.first_name, person.last_name)

    person.save()

This looks like the N+1 Query problem but maybe I'm wrong. I usually avoid this kind of code in my projects.

How many times does this hit the database?

Does the fact that it's in a migration (therefore a transaction) change anything?

Perhaps, the better way would be to do

Person.objects.update(name=Concat(F('first_name'), Value(' '), F('last_name')))

What's the correct way?

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