I have the following code that does not compile and returns this error:

error: could not find implicit value for parameter d: io.circe.Decoder[List[TableInfo]]

     r <- segmements.as[List[TableInfo]]

[Code]

import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
import io.circe.parser

val json: String =
"""
{
    "segmements": [
        {
            "tableName": "X",
            "segmentName": "XX",
            "pocs": [
                "[email protected]",
                "[email protected]"
            ]
        },
        {
            "tableName": "Y",
            "segmentName": "YY",
            "pocs": [
                "[email protected]",
                "[email protected]"
            ]
        }
    ]
}
"""

final case class TableInfo(tableName: String, segmentName: String)
object TableInfo {
  implicit final val TableInfoDecoder: Decoder[TableInfo] = deriveDecoder
}

val result = for {
  data <- parser.parse(json)
  obj <- data.asObject.toRight(left = new Exception("Data was not an object"))
  segmements <- obj("segmements").toRight(left = new Exception("Json didn't had the 
segments key"))
  r <- segmements.as[List[TableInfo]]
} yield r

println(result)

scastie link: https://scastie.scala-lang.org/BalmungSan/eVEvBulOQwGzg5hIJroAoQ/3

CodePudding user response：

Try this way

import io.circe.Decoder
import io.circe.generic.semiauto.deriveDecoder
import io.circe.parser
import io.circe._

val json: String =
"""
{
    "segments": [
        {
            "tableName": "X",
            "segmentName": "XX",
            "pocs": [
                "[email protected]",
                "[email protected]"
            ]
        },
        {
            "tableName": "Y",
            "segmentName": "YY",
            "pocs": [
                "[email protected]",
                "[email protected]"
            ]
        }
    ]
}
"""

final case class Tables(segments: List[TableInfo])
object Tables {
  implicit val decoder: Decoder[Tables] = (cursor: HCursor) =>
    for {
      segments          <- cursor.downField("segments").as[List[TableInfo]]
    } yield Tables(segments)
}

final case class TableInfo(tableName: String, segmentName: String)
object TableInfo {
  implicit final val TableInfoDecoder: Decoder[TableInfo] = deriveDecoder
}

val result = io.circe.parser.decode[Tables](json)

println(result)

CodePudding user response：

I added import import TableInfo._ to the code before val result as @ Luis Miguel Mejía Suárez recommended and the code worked as intended.