如何使用Play Framework JSON库为Map [Int，Int]创建JSON格式? [英] How do I create a JSON format for Map[Int, Int] using Play Framework JSON libs?

问题描述

我想使用Play Framework JSON库序列化Map[Int, Int].我想要类似的东西

I'd like to serialize a Map[Int, Int] using the Play Framework JSON libraries. I want something like

import play.api.libs.json._ implicit val formatIntMap = Json.format[Map[Int, Int]]

import play.api.libs.json._ implicit val formatIntMap = Json.format[Map[Int, Int]]

但是该代码得到了No unapply function found，我认为这是因为Map没有简单的案例类，所以没有提取器.

That code however gets an No unapply function found which I think is referring to the fact that there is no extractor for Map since it isn't a simple case class.

推荐答案

它将尝试制作JsObject，但由于将String映射到JsValue而不是将Int映射到JsValue而失败.您需要告诉它如何将密钥转换为字符串.

It will try to make a JsObject but is failing as it maps a String to a JsValue, rather than an Int to a JsValue. You need to tell it how to convert your keys into Strings.

  implicit val jsonWrites = new Writes[Map[Int, Int]] {
    def writes(o: Map[Int, Int]): JsValue = {
      val keyAsString = o.map { kv => kv._1.toString -> kv._2} // Convert to Map[String,Int] which it can convert
      Json.toJson(keyAsString)
    }
  }

这会将包含0-> 123的Map [Int，Int]转换为

This will turn a Map[Int, Int] containing 0 -> 123 into

JsObject(
    Seq(
        ("0", JsNumber(123))
    )
)

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