Question

我在解码JSON字符串中的可选字段时遇到了一些问题。我正在尝试解码＆＃34;规划＆＃34;计划可以是两种类型，正常计划或弹性计划。如果是正常计划，则它将具有planning_id，如果是灵活计划，则它将具有flexplanning_id。在我将存储计划的记录中，planningId和fiexplanningId都属于Maybe Int类型。

type alias Planning =
    { time : String
    , planningId : Maybe Int
    , groupId : Int
    , groupName : String
    , flex : Bool
    , flexplanningId : Maybe Int
    , employeeTimeslotId : Maybe Int
    , employeeId : Int
    }

这是我使用的解码器：

planningDecoder : Decoder Planning
planningDecoder =
    decode Planning
        |> required "time" string
        |> optional "planning_id" (nullable int) Nothing
        |> required "group_id" int
        |> required "group_name" string
        |> required "flex" bool
        |> optional "employee_timeslot_id" (nullable int) Nothing
        |> optional "flexplanning_id" (nullable int) Nothing
        |> required "employee_id" int

然而，解码器并不能准确地解码和存储来自JSON的数据。这是一个例子。这是我的应用程序发出的请求返回的字符串的一部分：

"monday": [
{
"time": "07:00 - 17:00",
"planning_id": 6705,
"group_name": "De rode stip",
"group_id": 120,
"flex": false,
"employee_timeslot_id": 1302,
"employee_id": 120120
},
{
"time": "07:00 - 17:00",
"group_name": "vakantie groep",
"group_id": 5347,
"flexplanning_id": 195948,
"flex": true,
"employee_id": 120120
}
],

然而，这是解码器的结果：

{ monday = [
  { time = "07:00 - 17:00"
  , planningId = Just 6705
  , groupId = 120
  , groupName = "De rode stip"
  , flex = False, flexplanningId = Just 1302
  , employeeTimeslotId = Nothing
  , employeeId = 120120 }
 ,{ time = "07:00 - 17:00"
  , planningId = Nothing
  , groupId = 5347
  , groupName = "vakantie groep"
  , flex = True
  , flexplanningId = Nothing
  , employeeTimeslotId = Just 195948
  , employeeId = 120120 
  }
 ],

正如您所看到的，在JSON中，有两个规划，一个具有planning_id，另一个具有flexplanning_id。但是，在解码器产生的记录中，第一个规划既有planningId又有flexplanningId，而第二个规则既没有。

Answer 1

您需要在解码器中翻转这两行以匹配它们的定义顺序：

|> optional "employee_timeslot_id" (nullable int) Nothing
|> optional "flexplanning_id" (nullable int) Nothing

它们按此顺序定义：

, flexplanningId : Maybe Int
, employeeTimeslotId : Maybe Int

Json.Decode.Pipeline麻烦可选

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