Cross validation in objects involving arrays: how to get the exact item that failed

[bettorinco]

Hello! Thanks in advance for considering my question :)

I have a doubt about cross field validation in an object schema with arrays inside.
Let's assume that I have this schema, representing an object with a basePath and an array of paths called assets:

const schema = object({
    basePath: string(),
    assets: array(string())
});

My goal is to check if the given assets (that I assume are all relative paths) exist when resolved against the basePath.

Since I do not have access to the basePath inside the array of assets, the obvious solution I found was to use a check on the whole object, to ensure that every asset was an existing path.

const schema = pipe(
   object({
       basePath: string(),
       assets: array(string())
   }),
   check(
       ({basePath, assets}) => assets.every(asset => fs.existsSync(path.resolve(basePath, asset))),
       "One of the assets does not exist."
   )
);

While this works as a validation, in case of error I am missing which one of the assets is invalid, since the check callback allows to only return a boolean and I am forced to throw a generic message as shown in the example.

So I'm wondering: is it possible to somehow intercept the exact path that gave the error?

Or even better: having a validation pipeline directly on the asset schema, is it somehow possible to access the "parent" object, so that I can use the basePath?

For example something like this, with a sort of context available in the validation fn:

const schema = object({
    basePath: string(),
    assets: array(
        pipe(
            string(),
            custom(
                (input, cxt) => fs.existsSync(path.resolve(cxt.basePath, input)),
                // Here would be the callback returning the error msg with the exact invalid path 
            )
        )
    )
});

Does anyone know a better approach to face this use case?
Thanks a lot in advance!

[fabian-hiller]

Hey, sorry for the late reply. Accessing the "parent" object is not possible but you can use rawCheck instead of check to have full control over the validation and the returned issues.