Elm:将具有单个元素的 JSON 数组解码为字符串 [英] Elm: Decode a JSON array with a single element into a string

问题描述

寻找类似的东西，但找不到确切的问题.

had a look for something like this, but can't find the exact issue.

我有一个从服务器端验证返回的 JSON，如下所示:

I have a JSON back from server side validation that looks like:

{ 
  "field": ["field-name"], 
  "messages":["message","message"]
}

我想做的是把它解码成一个榆树记录

What I would like to do is decode it into an elm record like

{ field: String, messages: List String }

但是，我在使用 err, field 字段时遇到了问题.我无法将单个元素 JSON 数组转换为该元素的字符串.

However, I'm having trouble with the err, field field. I'm having trouble turning a single element JSON array into just a string of that element.

是否甚至可以使用解码，或者我最好将其解码成一个列表，然后从列表中抓取头部.

Is it even possible with Decode, or am I better of Decoding it into a List and then just grabbing the head from the list.

这是我用来解码的:

valErrorDecoder : Decode.Decoder ValError
valErrorDecoder =
decode ValError
    |> required "field" (Decode.list Decode.string)
    |> required "messages" (Decode.list Decode.string)

感谢您的帮助！

推荐答案

试试Decode.index，应该可以解决问题.

Try Decode.index, that should do the trick.

valErrorDecoder : Decode.Decoder ValError
valErrorDecoder =
decode ValError
    |> required "field" (Decode.index 0 Decode.string)
    |> required "messages" (Decode.list Decode.string)

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