使用 Scala Argonaut 解析 JSON 数组 [英] Parse JSON array using Scala Argonaut

问题描述

我正在使用 Scala &Argonaut，尝试解析以下 JSON:

<预><代码>[{"name": "苹果","type": "水果",尺寸":3},{"name": "果酱","类型": "调味品",大小":5},{"name": "牛肉","类型": "肉",尺寸":1}]

并且正在努力解决如何迭代并将值提取到 List[MyType] 中，其中 MyType 将具有名称、类型和大小属性.

我很快会发布更具体的代码(我尝试了很多东西)，但基本上我想了解游标的工作原理，以及如何遍历数组等.我尝试使用 \\(downArray)移动到数组的头部，然后:->-遍历数组，然后--\(downField)不可用(至少 IntelliJ 不这么认为).所以问题是我该怎么做:

• 导航到数组
• 遍历数组(知道什么时候完成)
• 为每个字段提取字符串、整数等值 - jdecode[String]?as[String]?

解决方案

最简单的方法是为 MyType 定义一个编解码器.然后编译器会很高兴地为 List[MyType] 等构造一个解码器.我将在这里使用一个普通的类(不是案例类)来说明发生了什么:

class MyType(val name: String, val tpe: String, val size: Int)进口 argonaut._, Argonaut._隐式 def MyTypeCodec: CodecJson[MyType] = codec3((名称:字符串，tpe:字符串，大小:整数)=>新的 MyType(名称，tpe，大小)，(myType: MyType) =>(myType.name, myType.tpe, myType.size))("名称"、"类型"、"大小")

codec3 需要两个参数列表.第一个有两个参数，它们允许您告诉如何从 Tuple3 创建 MyType 的实例，反之亦然.第二个参数列表让您指定字段的名称.

现在您可以编写如下内容(如果 json 是您的字符串):

Parse.decodeValidation[List[MyType]](json)

大功告成.

I'm using Scala & Argonaut, trying to parse the following JSON:

[
    {
        "name": "apple",
        "type": "fruit",
        "size": 3
    },
    {
        "name": "jam",
        "type": "condiment",
        "size": 5
    },
    {
        "name": "beef",
        "type": "meat",
        "size": 1
    }
]

And struggling to work out how to iterate and extract the values into a List[MyType] where MyType will have name, type and size properties.

I will post more specific code soon (i have tried many things), but basically I'm looking to understand how the cursor works, and how to iterate through arrays etc. I have tried using \\ (downArray) to move to the head of the array, then :->- to iterate through the array, then --\ (downField) is not available (at least IntelliJ doesn't think so). So the question is how do i:

• navigate to the array
• iterate through the array (and know when I'm done)
• extract string, integer etc. values for each field - jdecode[String]? as[String]?

解决方案

The easiest way to do this is to define a codec for MyType. The compiler will then happily construct a decoder for List[MyType], etc. I'll use a plain class here (not a case class) to make it clear what's happening:

class MyType(val name: String, val tpe: String, val size: Int)

import argonaut._, Argonaut._

implicit def MyTypeCodec: CodecJson[MyType] = codec3(
  (name: String, tpe: String, size: Int) => new MyType(name, tpe, size),
  (myType: MyType) => (myType.name, myType.tpe, myType.size)
)("name", "type", "size")

codec3 takes two parameter lists. The first has two parameters, which allow you to tell how to create an instance of MyType from a Tuple3 and vice versa. The second parameter list lets you specify the names of the fields.

Now you can just write something like the following (if json is your string):

Parse.decodeValidation[List[MyType]](json)

And you're done.

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