#ZIO Query #ZQuery caching

zquery-caching.scala

import zio._
import zio.query._

case class DbDepartment(id: Int, name: String)
case class DbEmployee(id: Int, name: String, departmentId: Int)
case class Employee(name: String, departmentName: String)

case class GetDepartement(id: Int) extends Request[Nothing, DbDepartment]

object ZqueryDemo extends ZIOAppDefault {

  def run = {

    val employees = for {
      dbEmployees <- ZQuery.fromZIO(Repository.getAllEmployees)
      // for each employee I want departement info, but I don't want to query multiple time for the same departement
      employees <- ZQuery.foreachPar(dbEmployees)((e: DbEmployee) => {
        val department = ZQuery.fromRequest(GetDepartement(e.departmentId))(Repository.datasource)
        department.map(d => Employee(e.name, d.name))
      })
    } yield employees

    for {
      result <- employees.run
      _ <- ZIO.foreach(result)((e: Employee) => Console.printLine(e.toString))
    } yield ()
  }
}


object Repository {

  val datasource: DataSource[Any, GetDepartement] = DataSource.fromFunctionZIO("GetDepartement")((request: GetDepartement) => getDepartmentById(request.id))

  def getDepartmentById(id: Int) = {
    println("DB query : get department for dep Id " + id)
    ZIO.succeed(id match {
      case 1 => DbDepartment(1, "HR")
      case _ => DbDepartment(2, "IT")
    })
  }

  def getAllEmployees = {
    println("DB query : get all employees")
    ZIO.succeed(List(
      DbEmployee(1, "John", 1),
      DbEmployee(2, "Jane", 1),
      DbEmployee(3, "Bob", 2)
    ))
  }

}


/* Output : 
DB query : get all employees
DB query : get department for dep Id 2
DB query : get department for dep Id 1
Employee(John,HR)
Employee(Jane,HR)
Employee(Bob,IT)

Dept 1 is returned 2 times but query is only run one time (cached)

*/