Objects into JSON decoder through Elm ports

Question

I am passing an array of objects via ports into my Elm app. An example of an one of the objects in the array is:

{
    FullName: 'Foo Bar',
    Location: 'Here'
}

As you can see the keys in the object start with a capital, so I need to decode these in Elm. In my Elm code I have a type for the Person

type alias Person =
    { fullName : String
    , location : String
    }

and the port:

port getPeople : (List Json.Decode.Value -> msg) -> Sub msg

Finally I have a decoder (I am using Elm Decode Pipeline) to parse the data into the Person type.

peopleDecoder : Decoder Person
peopleDecoder =
    decode Person
        |> required "FullName" string
        |> required "Location" string

My question is how do I map the incoming port data into the Person type? I know I could do this in JS but I'd rather do it in my Elm code.

Answer 1

Json.Decode.decodeValue can decode a Json.Decode.Value, but it returns a Result String (List Person).

If you defined your Msg like this:

type Msg
    = GetPeople (Result String (List Person))

You could set up your subscription like this:

port getPeople : (Json.Decode.Value -> msg) -> Sub msg

subscriptions : Model -> Sub Msg
subscriptions model =
    getPeople (GetPeople << decodeValue (list peopleDecoder))

(Note that the first argument in the port has been changed to just a Value instead of List Value)