无法使用JSON Macro Inception将嵌套的JSON结构转换为Scala case类对象

Question

I have a requirement where the incoming JSON object is complex and mostly nested ex:

"users": {
  "utype": "PERSON",
  "language":"en_FR",
  "credentials": [
    {          
      "handle": "xyz@abc.com",
      "password": "123456",
      "handle_type": "EMAIL"
    }
  ],
  "person_details": {
    "primary": "true",
    "names": [
      {
      "name_type": "OFFICIAL",
      "title": "MR",
      "given": "abc",
      "family": "zat",
      "middle": "pqs",
      "suffix":"anathan"
     }
    ],
    "addresses": [
      {
        "ad_type": "HOME",
        "line1": "Residential 2211 North 1st Street",
        "line2": "Bldg 17",
        "city": "test",
        "county": "Shefield",
        "state" : "NY",
        "country_code": "xx",
        "postal_code": "95131"
      }
    ]
  }
}

For parsing this structure I use the below Case Classes

case class PersonUser (
    user_type:String,
    language_code:String,
    credentials:List[Credential],
    person_details:PersonDetails
)

case class Credential(handle:String, password:String,handle_type:String)

case class PersonDetails(
    primary_user:Boolean,
    names: List[Name],
    addresses:List[Address]
)

case class Name(
    name_type: String,
    title: String,
    given: String,
    family: String,
    middle: String,
    suffix:String
)

case class Address(
    address_type: String,
    line1: String,
    line2: String,
    city: String,
    county: String,
    state : String,
    country_code: String,
    postal_code: String
)

The statement to convert the json to scala case class object is failing:

implicit val testReads = Json.reads[PersonUser]

The errors says:

[scala-play-rest-example] $ compile
[info] Compiling 4 Scala sources to C:\Personal\Scala\scala-play-rest-example-master\target\scala-2.11\classes...
[error] C:\Personal\Scala\scala-play-rest-example-master\app\controllers\user\UserController.scala:16: **No implicit Reads for List[controllers.user.Credential], controllers.user.PersonDetails available.**
[error]     implicit val testReads = Json.reads[PersonUser]

Can someone please help me out to find out a way to represent complex json structure in Scala and convert it using Macro Inception or some other ways?

Answer 1

You need to create Reads for all of your case classes, not just the top-level. For instance:

case class Credential(handle:String, password:String,handle_type:String)

object Credential {

  implicit val reads = Json.reads[Credential]

}

Once you have those, Json.reads[PersonUser] will be able to work.

Answer 2

One other approach regarding the implicit reads/writes/format can be to define them in a separate helper object. Implicit in the object must be defined in a specific order like in your case the order of the implicit must be :-

object JsonHelper {
  implicit val nameReads = Json.reads[Name]
  implicit val addressReads = Json.reads[Address]  //position of 'nameReads' and 'addressReads' is interchangable
  implicit val credentialReads = Json.reads[Credential]
  implicit val personReads = Json.reads[PersonDetails]  // similarly position of 'credentialReads' and 'personReads' is interchangable
  implicit val personUserReads = Json.reads[PersonUser]  //'personUserReads' will always be the last
}

From the above code it can be learnt that the reads of case classe at the bottom of nesting hierarchy must be defined first, followed by the top case classes.

Now you just need to 'import JsonHelper._' in your service or wherever you are converting your JsValue to scala case class. :)