在播放框架 JsObject 中解析 Json 数组
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parsing a Json Array in play framework JsObject
提问by Zuriar
I have the following Json:
我有以下 Json：
{
"web-category" : "macaroons",
"sub-categories" : [
{ "name" : "pink" },
{ "name" : "blue" },
{ "name" : "green" }
]
}
I have got it in Play as a JsObject. So I can now successfully do the following:
我在 Play 中将它作为 JsObject 使用。所以我现在可以成功执行以下操作：
//(o is the JsObject)
val webCat:Option[String] = (o \ "web-category").asOpt[String]
println(webCat.toString)
>> Some(macaroons)
So far, so good. But how do I access the array Json objects? I have this...
到现在为止还挺好。但是如何访问数组 Json 对象呢？我有这个...
val subCats:Option[JsArray] = (o \ "sub-categories").asOpt[JsArray]
println(subCats.toString)
>> Some([{"name" : "blue"},{"name" : "green"},{"name" : "pink"}])
but what I need is to take the JsArray and get a List of all the names something like this:
但我需要的是获取 JsArray 并获取所有名称的列表，如下所示：
List("blue", "green", "pink")
Don't know how to access the JsArray thusly.
不知道如何访问 JsArray。
my thanks for your help in this.
我感谢你在这方面的帮助。
采纳答案by Travis Brown
I'd argue that it's generally a good idea to move from JSON-land to native-Scala-representation-land as early as possible. If objis your JsObject, for example, you can write this:
我认为尽早从 JSON-land 迁移到原生 Scala-representation-land 通常是个好主意。例如，如果obj是你的JsObject，你可以这样写：
val subCategories = (obj \ "sub-categories").as[List[Map[String, String]]]
val names = subCategories.map(_("name"))
Or even:
甚至：
case class Category(name: String, subs: List[String])
import play.api.libs.functional.syntax._
implicit val categoryReader = (
(__ \ "web-category").read[String] and
(__ \ "sub-categories").read[List[Map[String, String]]].map(_.map(_("name")))
)(Category)
And then:
进而：
obj.as[Category]
This latter approach makes error handling even cleaner (e.g. you can just replace aswith asOptat this top level) and composes nicely with other Readstype class instances—if you have a JsArrayof these objects, for example, you can just write array.as[List[Category]]and get what you expect.
后一种方法使错误处理更加清晰（例如，您可以在此顶层替换aswith asOpt）并与其他Reads类型的类实例很好地组合——例如，如果您有JsArray这些对象中的一个，您就可以编写array.as[List[Category]]并获得您期望的内容。
回答by johanandren
What Peter said, or:
彼得所说的，或：
(o \ "sub-categories" \ "name").map(_.as[String]).toList
回答by Peter
Something like this:
像这样的东西：
subCats.map( jsarray => jsarray.value.map(jsvalue => (jsvalue \ "name").as[String]).toList)
This will normally return a Option[List[String]]
这通常会返回一个 Option[List[String]]
