Reputation: 45
I'm trying to use circe to decode a JSON object into a list of objects. I only want to use some of the fields of the JSON response to create the object, so I feel like I have to create a custom decoder.
The class I want to make a sequence of is defined as follows:
case class Review(Id: String, ProductId: String, Rating: Int)
I tried creating a custom decoder like this:
implicit val reviewDecoder: Decoder[Review] = Decoder.instance { c =>
val resultsC = c.downField("Results")
for {
id <- resultsC.downArray.get[String]("Id")
productId <- resultsC.downArray.get[String]("ProductId")
rating <- resultsC.downArray.get[Int]("Rating")
} yield Review(id, productId, rating)
}
reviewDecoder.decodeJson(json)
seems to result in only doing the first result and not all of them.
I have a JSON response like this:
{
"Limit":2,
"Offset":0,
"TotalResults":31,
"Locale":"en_US",
"Results":
[
{"Id":"14518388",
"CID":"21a9436b",
"ProductId":"Product11",
"AuthorId":"jcknwekjcnwjk",
"Rating":3
},
{"Id":"14518035",
"CID":"8d67b6f5",
"ProductId":"Product11",
"AuthorId":"fnkjwernfk",
"Rating":3
}
],
"Includes":{},
"HasErrors":false,
"Errors":[]}
I want to be able to parse this JSON object using circe to create a Seq[Review], but I'm stumped how.
****Edit** Luis' answer does answer this question but say I have a more complicated class I want to create a sequence of:
case class User(id: Int)
case class Review(user: User, ProductId: String, Rating: Int)
How would I be able to create a sequence of Reviews in this case?
Upvotes: 1
Views: 1055
Reputation: 22895
I would just use the cursor to getting the Array and then use the generic decoder.
The following code was tested on ammonite, where json
is a string containing your sample input.
import $ivy.`io.circe::circe-core:0.11.1`
import $ivy.`io.circe::circe-generic:0.11.1`
import $ivy.`io.circe::circe-parser:0.11.1`
import io.circe.{Decoder, Jsom}
import io.circe.parser.parse
final case class Review(Id: String, ProductId: String, Rating: Int)
implicit val reviewDecoder: Decoder[Review] = io.circe.generic.semiauto.deriveDecoder
parse(json).getOrElse(Json.Null).hcursor.downField("Results").as[List[Review]]
// res: io.circe.Decoder.Result[List[Review]] = Right(List(Review("14518388", "Product11", 3), Review("14518035", "Product11", 3)))
Upvotes: 1