getting unique id

[Larry Martell]

I have an app that needs to get a unique ID. Many threads run at the
same time that need one. I would like the IDs to be sequential. When I
need a unique ID I do this:

with transaction.atomic():
max_batch_id =
JobStatus.objects.select_for_update(nowait=False).aggregate(Max('batch_id'))
json_dict['batch_id'] = max_batch_id['batch_id__max'] + 1
status_row = JobStatus(**json_dict)
status_row.save()

But multiple jobs are getting the same ID. Why does the code not work
as I expect? What is a better way to accomplish what I need?

[Shaheed Haque]

Are all the threads in the same Python process? Or the same machine? Do they have to persist across process (or machine) restarts? 

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[Larry Martell]

On Wed, Nov 23, 2022 at 1:43 PM Shaheed Haque <shahee...@gmail.com> wrote:
>
> Are all the threads in the same Python process?

No

> Or the same machine?

No

> Do they have to persist across process (or machine) restarts?

Yes.

Playing around with using F() but still don't have it working as desired.

[Thomas Lockhart]

Why not use the existing Django AutoField?

- Tom

[Larry Martell]

On Wed, Nov 23, 2022 at 3:01 PM Thomas Lockhart <tlockh...@gmail.com> wrote:
>
> Why not use the existing Django AutoField?

Because I have multiple rows with the same batch_id, and also I would
like the batch_ids to be sequential.

The use case is a batch job dashboard. Users run jobs that spawn many
sub jobs. The jobs all record their status in the JobStatus table. The
batch dashboard shows all the sub jobs grouped under their parent job.
The parent job creates a row with a new batch_id, and that is passed
to the sub jobs. They all record their status using that same batch
id, but each in its own row.

[Larry Martell]

I ended up using another table to get the batch_ids from. It works,
but I still wonder how to make it work without a second table.