The point is, I have to distinguish between an instance which is
created, but its save method is not yet called. And an instance coming
from the database via a manager.
bg,
Johannes
On 16.01.2014 16:04, Erik Cederstrand wrote:
Den 16/01/2014 kl. 14.27 skrev Johannes Schneider
<johannes.schnei...@galileo-press.de>:
Hi List,
I need to check, if a given instance of a Model already exists in the Database.
I cannot check 'instance.pk is None', because there are manually given PKs (no
discussion about this plz).
Up to now I check if 'instance._state.adding' is true. But I don't like this
solution.
Checking 'InstanceModel.objects.exists(pk=self.pk)' generates too much queries,
so this is not acceptable in my case.
Can you elaborate on “too much queries”? exists() is supposed to be the
cheapest way of checking if the object exists. It seems like you want to check
the database, without actually checking the database…
If you want to check a large number of objects at the same time, just do
something like:
InstanceModel.objects.filter(id__in=(your, list, of,
PKs)).values_list('id', flat=True)
to get all pre-existing PKs in one query.
Erik
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