Hi, I am having a real hard time getting SourceAssets to work. They just don't seem to get any data for the downstream assets, clearly I have missed a concept / got something wrong in my code. I have an existing table in a database which I have a custom io manager for. The below code defines this existing table as a source asset which is then used in a downstream asset as an input, to move it to a different sql server.

rdw_org_loc_dm = SourceAsset(io_manager_key="rdw_io_manager", key=AssetKey("rdw_org_loc_dm"))


@asset(io_manager_key="sql_server_io_manager", key_prefix=["ref", str(orgSys + "_" + orgTable)])
def rdw_org_loc_dm_to_sql(rdw_org_loc_dm: pd.DataFrame):
    df = rdw_org_loc_dm
    return Output(  # The return value is updated to wrap it in `Output` class
        value=df,  # The original df is passed in with the `value` parameter
        metadata={
            "num_records": len(df),  # Metadata can be any key-value pair
            "preview": MetadataValue.md(df.head().to_markdown()),
            # The `MetadataValue` class has useful static methods to build Metadata
        }
    )

The defs is as follows....

defs = Definitions(
    assets=all_assets,
    jobs=[stock_job],

    resources={
        
        "sql_server_io_manager": sql_server_io_manager.SQLServerIOManager(
            user=EnvVar("SQL_USER"),
            password=EnvVar("SQL_PASSWORD"),
            database="db_Staging",
            table="dim_date"
            ),
        "rdw_io_manager": rdw_io_manager.RDWIOManager(
         table= "rdw_org_loc_dm"
            )
    },
)

The error I get when I run the job is the screenshot below. No extra errors in the console. It doesn't try to use the io manager as far as I can tell. I am really stumped, any help would be appreciated. Or a working example?

It appears your df is a NoneType. Instead of trying to preload the asset, set the asset io_manager_key to your custom io manager which will load the asset input with it. Then just specify the output io manager https://docs.dagster.io/concepts/io-management/io-managers#per-asset-io-manager