Scala / Play如何使用JSON读取来处理可以是字符串或数组的JSON值，并始终返回Set [String]

Question

I have the following class in my play server and the JSON Reads used for validation

case class Foo(name: String, link: String)

val fooReads = (
  (__ \ "name").read[String] ~
  (__ \ "link").read[String]
)(Foo.apply _)

I have changed the model to allow multiple links instead of one so i can expect array of strings in the input JSON:

case class Foo(name: String, link: Set[String])

val fooReads = (
  (__ \ "name").read[String] ~
  (__ \ "link").read[Set[String]] // it works this way
)(Foo.apply _)

I want to make it back compatible so it can handle JSON value of "link" with string along with array of strings

Answer 1

You can use the operator orElse on json Reads to create your custom reader:

val readsSet: Reads[Set[String]] = Reads.of[Set[String]].orElse(Reads.of[String].map(str => Set(str)))

val fooReads = (
  (__ \ "name").read[String] ~
  (__ \ "link").read[Set[String]](readsSet)
)(Foo.apply _)

Answer 2

You can use Reads.orElse combinator:

val fooReads: Reads[Foo] = (
  (__ \ "name").read[String] ~
  (__ \ "link").read(Reads.of[String].map(str => Set(str)).
    orElse(Reads.of[Set[String]]))
)(Foo.apply _)