Elm

Question

给定 JSON 个对象列表，例如：

[{"id":"1", "name":"Jane"},{"id":"2", "name":"Joe"}]

如何将其解码为 Dict String Foo，其中 id 作为键，其中 Foo 是 {id: String, name: String} 类型的记录？（请注意，该记录还包含 id。）

Answer 1

例如使用以下组合：

Json.Decode.list (https://package.elm-lang.org/packages/elm/json/latest/Json-Decode#list
Json.Decode.map2 (https://package.elm-lang.org/packages/elm/json/latest/Json-Decode#map2)
Dict.fromList (https://package.elm-lang.org/packages/elm/core/latest/Dict#fromList)
Tuple.pair (https://package.elm-lang.org/packages/elm/core/latest/Tuple#pair)


import Dict exposing (Dict)
import Json.Decode as Decode exposing (Decoder)

type alias Foo =
    { id : String, name : String }

fooDecoder : Decoder Foo
fooDecoder =
    Decode.map2 Foo (Decode.field "id" Decode.string) (Decode.field "name" Decode.string)

theDecoder : Decoder (Dict String Foo)
theDecoder =
    Decode.list (Decode.map2 Tuple.pair (Decode.field "id" Decode.string) fooDecoder)
        |> Decode.map Dict.fromList

Elm - 如何将 json 对象列表解码为字典

Elm - How to decode a json list of objects into a Dict

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