解碼包含物件列表的物件列表

*請參閱 Ellie 的工作示例。*此示例使用 NoRedInk / elm-decode-pipeline 模組。

給定一個 JSON 物件列表，它們本身包含 JSON 物件列表：

[
  {
    "id": 0,
    "name": "Item 1",
    "transactions": [
      { "id": 0, "amount": 75.00 },
      { "id": 1, "amount": 25.00 }
    ]
  },
  {
    "id": 1,
    "name": "Item 2",
    "transactions": [
      { "id": 0, "amount": 50.00 },
      { "id": 1, "amount": 15.00 }
    ]
  }
]

如果上面的字串在 payload 字串中，則可以使用以下程式碼解碼：

module Main exposing (main)

import Html exposing (..)
import Json.Decode as Decode exposing (Decoder)
import Json.Decode.Pipeline as JP
import String

type alias Item =
    { id : Int
    , name : String
    , transactions : List Transaction
    }

type alias Transaction =
    { id : Int
    , amount : Float
    }

main =
    Decode.decodeString (Decode.list itemDecoder) payload
        |> toString
        |> String.append "JSON "
        |> text

itemDecoder : Decoder Item
itemDecoder =
    JP.decode Item
        |> JP.required "id" Decode.int
        |> JP.required "name" Decode.string
        |> JP.required "transactions" (Decode.list transactionDecoder)

transactionDecoder : Decoder Transaction
transactionDecoder =
    JP.decode Transaction
        |> JP.required "id" Decode.int
        |> JP.required "amount" Decode.float