Hey Erik,
What Django version are you on?
On Tuesday, May 24, 2016 at 1:28:57 AM UTC+5:30, Erik Cederstrand wrote:
>
> Hi,
>
> I have inherited a legacy Item model that has a composite unique key
> consisting of a Customer ID and a per-customer, incrementing Item ID.
> Assume I can't change the model.
>
> On inserts, the legacy code would let the database increment the Item ID
> to avoid race conditions. Something like this:
>
> INSERT INTO item_table (customer_id, item_id, name, ...) VALUES (123,
> (SELECT MAX(item_id) FROM item_table WHERE customer_id =123) + 1, 'MyItem',
> ...);
>
>
> Is there any way I can do the same using the Django ORM without opening up
> for race conditions? I.e. something better than:
>
> i = Item(customer_id=123, name='MyItem', ...)
> i.item_id =
> Item.objects.filter(customer_id=123).aggregate(Max('item_id'))['item_id__max']
>
> + 1
> i.save()
>
> Or do I just wrap that in a loop and catch IntegrityError if I don't want
> to use raw SQL?
>
>
> Thanks,
> Erik
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