ELM how to decode different value in json array - arrays

Question

I have a JSON array with different value in the array and I don't know how to parse it. Here is an example:
[
{
"firstname": "John",
"lastname": "Doe",
"age": 30
},
{
"companyName": "Doe enterprise",
"location": "NYC",
"numberOfEmployee": 10
}
]
So my JSON is like this, the first element of the array is an user, and the second a company.
I have the equivalent in Elm:
type alias User =
{ firsname : String
, lastname : String
, age : Int
}
type alias Company =
{ companyName : String
, location : String
, numberOfEmployee : Int
}
then: Task.perform FetchFail FetchPass (Http.get decodeData url).
So how do I get my User and Company pass in my FetchPass function ?
There is something like Json.Decode.at but it's for object only.
Here there a way to do something like this ?
decodeData =
Json.at [0] userDecoder
Json.at [1] companyDecoder

Answer 1

Json.at works for array indexes as well. First you'll need a Data type to hold the user and company:
import Json.Decode as Json exposing ((:=))
type alias Data =
{ user : User
, company : Company
}
And you'll need simple decoders for user and company:
userDecoder : Json.Decoder User
userDecoder =
Json.object3 User
("firstname" := Json.string)
("lastname" := Json.string)
("age" := Json.int)
companyDecoder : Json.Decoder Company
companyDecoder =
Json.object3 Company
("companyName" := Json.string)
("location" := Json.string)
("numberOfEmployee" := Json.int)
And finally you can use Json.at to get the values at those array indexes. The difference from your example is that you need to pass a string containing an integer index instead of an int:
dataDecoder : Json.Decoder Data
dataDecoder =
Json.object2 Data
(Json.at ["0"] userDecoder)
(Json.at ["1"] companyDecoder)