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Title
# ask-community
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Aaron T

03/29/2023, 2:35 PM
If I have a daily partition, and a downstream asset that gets a
TimeWindowPartitionMapping
of the upstream partition with the
start_offset=-1
when I go to backfill, the first partition of the time windowed asset will fail to materialize because there is no upstream partition with a -1 offset. I tried a different partition start date, for the partition definition, but dagster would not allow different partition start dates. Is there anyway to have this so that the time window partition mapping knows it cannot get the first partition and excludes it from backfilling?
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claire

03/29/2023, 11:51 PM
Hi Aaron. I think this would be good default behavior. I'd recommend filing an issue so we can track it and add this to our backlog.
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Aaron T

03/30/2023, 2:51 PM
Hi @claire I submitted an feature request - https://github.com/dagster-io/dagster/issues/13255. I would be interested in trying to contribute and open a PR. If you are able to offer some guidance on where you think changes need to be made I can take a look. Thanks.
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claire

03/30/2023, 5:01 PM
Thanks Aaron! Responded back on the issue, but I actually tried this out and it was working--it might have been fixed in a recent version. I'd recommend upgrading to the latest version and trying this out, let me know if you're still experiencing this issue
p

Philippe Laflamme

03/30/2023, 5:08 PM
FYI: I believe this thread is somewhat related to the problem, specifically about this part
I tried a different partition start date, for the partition definition, but dagster would not allow different partition start dates.
Having the ability to create a job that targets assets that only differ by start/end offsets would solve this problem as well, since you could (presumably) backfill that job.
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