QuillProblem.sc

import $ivy.`io.getquill::quill-jdbc:3.5.1`, io.getquill._
val ctx: PostgresJdbcContext[LowerCase.type] = ???

import ctx._

case class CountryLanguage(countryCode: String,
                            language: String,
                            isOfficial: Boolean,
                            percentage: Double)
case class City(id: Int,
                 name: String,
                 countryCode: String,
                 district: String,
                 population: Int)

val popularLanguages = ctx.run(
  query[City]
    .join(query[CountryLanguage])
    .on { case (city, language) => city.countryCode == language.countryCode }
    .groupBy { case (city, language) => language }
    .map{case (language, cityLanguages) => (language, cityLanguages.size)}
    .sortBy{case (language, cityCount) => (language, -cityCount)}
    .take(5)
)

pprint.log(popularLanguages)

// java.lang.IllegalStateException: 
// The monad composition can't be expressed using applicative joins. 
// Faulty expression: '(x01, x11).size'. Free variables: 'List(x01, x11)'.
// at io.getquill.util.Messages$.fail(Messages.scala:43)
// at io.getquill.context.sql.idiom.SqlIdiom.$anonfun$translate$1(SqlIdiom.scala:43)
// at scala.Option.map(Option.scala:242)
// at io.getquill.context.sql.idiom.SqlIdiom.translate(SqlIdiom.scala:43)
// at io.getquill.context.sql.idiom.SqlIdiom.translate$(SqlIdiom.scala:33)
// at io.getquill.PostgresDialect$.translate(PostgresDialect.scala:43)
// at io.getquill.context.ContextMacro.translateStatic(ContextMacro.scala:51)
// at io.getquill.context.ContextMacro.translate(ContextMacro.scala:37)
// at io.getquill.context.ContextMacro.expand(ContextMacro.scala:24)
// at io.getquill.context.ContextMacro.expand$(ContextMacro.scala:21)
// at io.getquill.context.QueryMacro.expand(QueryMacro.scala:8)
// at io.getquill.context.QueryMacro.expandQueryWithMeta(QueryMacro.scala:184)
// at io.getquill.context.QueryMacro.expandQuery(QueryMacro.scala:51)
// at io.getquill.context.QueryMacro.runQuery(QueryMacro.scala:34)
//
// val popularLanguages = ctx.run(
//   ^