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

看起来像这样，但是找不到确切的问题。

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

我从服务器端验证返回了一个JSON，如下所示：

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

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

我想做的就是将其解码为像这样的榆树记录

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

{ field: String, messages: List String }

但是，我遇到了错误的字段字段。我在将单个元素的JSON数组转换为该元素的字符串时遇到麻烦。

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.

使用Decode甚至可能，还是最好将其解码为列出，然后从列表中抢先。

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.

这就是我要解码的内容：

This is what I have for the decode:

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

尝试 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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