can you join two tables and result with an obj (from first table) containing a list of obj(from the second table) - sql

Question

First of all my code:
Table 1:
object Company : Table() {
val name = varchar("pk_name", 250)
override val primaryKey = PrimaryKey(name, name = "pk_company_constraint")
}
Table 2&3:
object Sector : IntIdTable() {
val name = varchar("fk_name", 50).references(MainSector.name)
val alias = varchar("alias", 50).nullable()
val companyName = varchar("fk_company_name", 250).references(Company.name, onDelete = ReferenceOption.CASCADE)
}
object MainSector : Table() {
val name = varchar("pk_name", 50)
override val primaryKey = PrimaryKey(name, name = "pk_main_sector_constraint")
}
My Problem:
I need to parse the result into a DTO that looks like this:
data class CompanyDTO (
val companyName: String,
val sectorList: List<SectorDTO>
)
data class SectorDTO (
val mainSectorName: String,
val sectorAlias: String
)
I am able to get a Company with the first Sector from the database, but i have no idea how to get a list of them.
My try:
override fun retrieveCompanies(vararg names: String): List<CompanyDTO> {
var retlist: List<CompanyDTO> = emptyList()
if (names.isEmpty()){
retlist = transaction {
(Company innerJoin Sector)
.select{Company.name eq Sector.companyName}
.map { CompanyDTO(it[Company.name], listOf(
SectorDTO(it[Sector.name], it[Sector.alias]?: "")
)) }
}
} else {
//return specific
}
return retlist
}
If no arguments are given i want to return all companies from the database, if arguments are given i want to return only companies with given name.
I can´t find anything about this topic in the official documentation, please send help

Answer 1

If Company could not have any Sector you need to use leftJoin and then your code could be like:
Company.leftJoin.Sector.selectAll().map {
val companyName = it[Company.name]
val sector = it.tryGet(Sector.name)?.let { name ->
SectorDTO(name, it[Sector.alias].orEmpty())
}
companyName to sector
}.groupBy({ it.first }, { it.second }).map { (companyName, sectors) ->
CompanyDTO(companyName, sectors.filterNotNull())
}