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# ask-community
s

Sergio Pintaldi

04/04/2023, 11:38 PM
Quick question about
multi_asset
: I want to define a multi asset because the output is generated using the same op/logic. So I went on and define a
multi_asset
as below
Copy code
from dagster import AssetIn, AssetKey, AssetOut, Output, multi_asset


@multi_asset(
    name="my_op",
    ins={
        "in_a": AssetIn("complex_name_for_input_a"),
        "in_b": AssetIn("complex_name_for_input_b"),
    },
    outs={"a": AssetOut(is_required=False), "b": AssetOut(is_required=False)},
    internal_asset_deps={
        "a": {AssetKey("complex_name_for_input_a")},
        "b": {AssetKey("complex_name_for_input_b")},
    },
    can_subset=True,
)
def my_complex_assets(context, in_a, in_b):
    out_value = None
    out_name = None
    if "a" in context.selected_output_names:
        out_name = "a"
        out_value = in_a + 1

    if "b" in context.selected_output_names:
        out_name = "b"
        out_value = in_b + 1

    if out_value is not None and out_name is not None:
        yield Output(value=a + 1, output_name="a")
The issue that I am facing is that when selecting and materialising one output, let's say
"a"
, the op needs to read both the inputs, but if they do not exists, it fails. I hoped it needed to read only the one required by the respective output. With that I was thinking of achieving the logic "if this input do this output". What can I do to achieve this logic? Separate into single assets wrapping the internal logic into a python function?
s

sandy

04/05/2023, 12:10 AM
Separate into single assets wrapping the internal logic into a python function?
This seems like a reasonable approach to me Feel free to file a github issue with this request. I think the main question is what Dagster would pass as a parameter value into the function for the inputs that aren't needed.
🙏 1
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