How is the ` asset` decorator s `io manager key` parameter s

Question

How is the ` asset` decorator s `io manager key` parameter supposed to work I can t seem to get it to recognize a custom IOManager even with a very minimal case code in thread

Spencer Nelson · Answer

This is the bare minimum taken from examples ```class MyIOManager IOManager def get path self context gt str return join context asset key path def handle output self context obj pass def load input self context return 1 io manager def my io manager init context return MyIOManager asset io manager key= my io manager def my asset context pass``` When I try to load this I get an error

Spencer Nelson · Answer

```dagster core errors DagsterInvalidDefinitionError io manager with key my io manager required by output result of op my asset was not provided Please provide a lt class dagster core storage io manager IOManagerDefinition gt to key my io manager or change the required key to one of the following keys which points to an lt class dagster core storage io manager IOManagerDefinition gt io manager ```

Spencer Nelson · Answer

I will note that using `io manager def` works for example ``` asset io manager def=my io manager def my asset context pass```

Spencer Nelson · Answer

But that parameter is marked as experimental so I wont use it until it s released

Zach · Answer

are you mapping your IO manager to your asset in your definition otherwise I don t think Dagster knows what IO manager to use the io manager key argument is just a string that dagster uses to look up what resource definition key to look for the io manager in <https docs dagster io concepts io management io managers per asset io manager|see this example>

Spencer Nelson · Answer

Adding ```defs = Definitions assets= my asset resources= my io manager my io manager ``` at the end of the file has no effect

Spencer Nelson · Answer

Here is the complete file which errors with the same error I posted above ```from dagster import asset IOManager io manager Definitions class MyIOManager IOManager def get path self context gt str return join context asset key path def handle output self context obj pass def load input self context return 1 io manager def my io manager init context return MyIOManager asset io manager key= my io manager def my asset context pass defs = Definitions assets= my asset resources= my io manager my io manager ```

Spencer Nelson · Answer

This remains a problem for me Should I make a Github issue since this is more about the Python API

Alec Koumjian · Answer

< Spencer Nelson> Howdy friend Just FYI I think we have this working properly now The thing that breaks is if you try to create a ` job` it will not properly load the resource definitions However if you use `define asset job` it loads in the global resource definitions just fine