scala 读取配置到案例类地图的地图

Question

I need to read from a config file and map the config to a case class .It works fine if i have one table as below

CONFIG

mapping {
   target {
     oracle  = {
         type = "oracle"
         schema    = "orcl"
         tableName = "my_table"
         query = "select key from my_table where dob='2020-01-01'
     }
}

SCALA CODE SNIPPET

 val targetConfig:Map[String,QueryEngine] = config.getObject("mapping.target")
    .entrySet()
    .asScala
    .foldLeft(Map.empty[String , QueryEngine]) { case ( acc , entry ) =>
      val target = entry.getKey
      val targetConfig = entry.getValue match {
        case validElement if validElement.valueType() == ConfigValueType.OBJECT  => validElement.asInstanceOf[ConfigObject].toConfig
        case invalidElement => sys.error("illegal syntax at $invalidElement")
      }

      targetConfig.getString("type")    match {

        case "oracle" => acc + (target ->  new OracleQueryEngine(vars,target,targetConfig.getString("schema"),targetConfig.getString("tableName"),targetConfig.getString("query"),targetConfig.getString("param")))

        case  x   => sys.error(s"unknow target not defined $targetConfig with $targetConfig")
      }
    }

NOW i updated CONFIG with MULTIPLE tables in the target mapping.

mapping {
   target {
     oracle  =   
        emp = {
         type = "oracle"
         schema    = "orcl"
         tableName = "emp"
         query = "select key from emp where dob='2020-01-01'
        }
        dept = {
         type = "oracle"
         schema    = "orcl"
         tableName = "dept"
         query = "select key from dept where dob='2020-01-01'
        }
    }
}

CODE SNIPPET for the multiple table scenario This is giving error Expression of mutable.Set[Map[String,QueryEngine]] doesnt confirm to Map[Query,String]

 val targetConfig:Map[String,QueryEngine] = config.getObject("mapping.target")
    .entrySet()
    .asScala
    .foldLeft(Map.empty[String , QueryEngine]) { case ( acc , entry ) =>
      val target = entry.getKey
      val targetConfig = entry.getValue match {
        case validElement if validElement.valueType() == ConfigValueType.OBJECT  => validElement.asInstanceOf[ConfigObject].toConfig
        case invalidElement => sys.error("illegal syntax at $invalidElement")
      }
      targetConfig.getObject(s"mapping.target.$target").keySet().asScala.map { key =>
        target  match {
          case "oracle" => acc + (target ->  new OracleQueryEngine(vars,target,targetConfig.getString("schema"),targetConfig.getString("tableName"),targetConfig.getString("query"),targetConfig.getString("param")))

          case  x   => sys.error(s"unknow target not defined $targetConfig with $targetConfig")
        }
      }

  }

PURE CONFIG CODE

import pureconfig._
import pureconfig.generic.ProductHint
import pureconfig.generic.auto._
import com.typesafe.config.ConfigFactory
import pureconfig._
import pureconfig.generic.auto._

object PureconfigExample {

  case class QueryEngine(`type`: String, schema: String, tableName: String, query: String)
  type  DatabaseConfig = Map[String, Map[String, QueryEngine]]
  case class TargetConfig(target: DatabaseConfig)
  case class ApplicationConfig(mapping: TargetConfig)

  def main(args: Array[String]): Unit = {
    val configString =
      """
        |mapping {
        |   target {
        |     oracle {
        |        emp {
        |         type = "oracle"
        |         schema    = "orcl"
        |         tableName = "emp"
        |         query = "select key from emp where dob='2020-01-01'"
        |        }
        |        dept  {
        |         type = "oracle"
        |         schema    = "orcl"
        |         tableName = "dept"
        |         query = "select key from dept where dob='2020-01-01'"
        |        }
        |      }
        |    }
        |}
        |""".stripMargin

    import pureconfig.generic.auto._

    // See for more details - https://pureconfig.github.io/docs/overriding-behavior-for-case-classes.html
    implicit def hint[T]: ProductHint[T] = ProductHint[T](ConfigFieldMapping(CamelCase, CamelCase))

    val config = ConfigSource.string(configString).load[ApplicationConfig]
    println(config)
  }
}

POM.XML

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test2</groupId>
    <artifactId>test2</artifactId>
    <version>1.0-SNAPSHOT</version>


<dependencies>
    <dependency>
        <groupId>com.github.pureconfig</groupId>
        <artifactId>pureconfig-generic-base_2.12</artifactId>
        <version>0.12.2</version>
    </dependency>
    <dependency>
        <groupId>com.github.pureconfig</groupId>
        <artifactId>pureconfig-generic_2.12</artifactId>
        <version>0.12.0</version>
    </dependency>
</dependencies>

</project>

COMPILER ERROR

PureConfigExample.scala
Error:(43, 56) Cannot find an implicit instance of pureconfig.ConfigReader[PureconfigExample.ApplicationConfig].
If you are trying to read or write a case class or sealed trait consider using PureConfig's auto derivation by adding `import pureconfig.generic.auto._`
    val config = ConfigSource.string(configString).load[ApplicationConfig]
Error:(43, 56) not enough arguments for method load: (implicit reader: pureconfig.Derivation[pureconfig.ConfigReader[PureconfigExample.ApplicationConfig]])pureconfig.ConfigReader.Result[PureconfigExample.ApplicationConfig].
Unspecified value parameter reader.
    val config = ConfigSource.string(configString).load[ApplicationConfig]

Answer 1

Excuse me, for probably, not the answer you probably expected, but I strongly encourage avoid manual config parsing, because there are tools that doing it for you automatically, without boiler-plate code and type-safe at the same time. The most popular and probably the best library in Scala eco-system is PureConfig . So in you case the solution would look like something like this:

import pureconfig._
import pureconfig.generic.ProductHint
import pureconfig.generic.auto._

object PureconfigExample {

  case class QueryEngine(`type`: String, schema: String, tableName: String, query: String)
  type  DatabaseConfig = Map[String, Map[String, QueryEngine]]
  case class TargetConfig(target: DatabaseConfig)
  case class ApplicationConfig(mapping: TargetConfig)

  def main(args: Array[String]): Unit = {
    val configString =
      """
        |mapping {
        |   target {
        |     oracle {
        |        emp {
        |         type = "oracle"
        |         schema    = "orcl"
        |         tableName = "emp"
        |         query = "select key from emp where dob='2020-01-01'"
        |        }
        |        dept  {
        |         type = "oracle"
        |         schema    = "orcl"
        |         tableName = "dept"
        |         query = "select key from dept where dob='2020-01-01'"
        |        }
        |      }
        |    }
        |}
        |""".stripMargin

    // See for more details - https://pureconfig.github.io/docs/overriding-behavior-for-case-classes.html
    implicit def hint[T]: ProductHint[T] = ProductHint[T](ConfigFieldMapping(CamelCase, CamelCase))

    val config = ConfigSource.string(configString).load[ApplicationConfig]
    println(config)
  }
}

which in my case produces next result:

Right(ApplicationConfig(TargetConfig(Map(oracle -> Map(emp -> QueryEngine(oracle,orcl,emp,select key from emp where dob='2020-01-01'), dept -> QueryEngine(oracle,orcl,dept,select key from dept where dob='2020-01-01'))))))

Hope this help!