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# ask-community
j

Jeff Nawrocki

02/21/2023, 8:27 PM
Hello! I am trying to build a pipeline that triggers when a file on S3 is updated by checking it's
Last Modified
timestamp, following this example:

https://www.youtube.com/watch?v=PXN3zJJbjWg&t=186s

. This example uses
@observable_source_asset
to pull the timestamp and the subsequent assets get marked as
Stale
if the file is updated. It looks like I can use a Freshness Policy to run the stale assets, however, is there a way to have the
@observable_source_asset
check the timestamp without having to interact with it? Ideally, this process would work automatically.
Adding a
asset_reconciliation_sensor
doesn't seem to help.
Copy code
defs = Definitions(
    assets=[asset1, asset2, asset3, asset4],
    sensors=[
        build_asset_reconciliation_sensor(
            asset_selection=AssetSelection.assets(asset1, asset3, asset4),
            name="asset_reconciliation_sensor",
        ),
    ],
)
Downstream assets still appear stale or overdue (if using freshness policy) when using this.