Hi everyone, nice to meet you all. I've a doubt: Suppose i have an @op without output, but with an asset materialization.

@op(ins={"path": In(str)})
def my_op(conxtext, path):
    metadata = load_file_into_data_lake(path)
    yield AssetMaterialization(
        asset_key=AssetKey(metadata["index"]),
        metadata=metadata
    )

it raises an error:

dagster.core.errors.DagsterStepOutputNotFoundError: Core compute for op "<op_name>" did not return an output for non-optional output "result"

. I imagine that the asset materialization event requires an output, is that true? Nevertheless i found a workaround with:

@op(
    ins={"path": "<cloud://cloud_path>"},
    out={"result": Out(Nothing)}  # workround
)
def my_op(conxtext, path):
    ...

Thanks!

I forget where, but I recall reading that if an asset is yielded, an output must also be yielded, so that’s a reasonable workaround. Sometimes, I’ll just put a

yield Output(True)

on ops that materialize assets but don’t need to actually return anything; your approach is likely better 🙂

Alex's answer is correct, but another option is to use

context.log_event(AssetMaterialization(...))

instead of yielding the event.

Thanks you all! I'll switch to Owen's approach, definitely cleaner.