How can I serialize kotlin exposed sql dao

Question

I use kotlin exposed sql in my project I created kotlin object for my table also I created DAO as is in example all working as should, but when I want return List of my DAO objects I get:

com.fasterxml.jackson.databind.JsonMappingException: Infinite recursion (StackOverflowError) (through reference chain: org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]->java.util.ArrayList[0]->org.jetbrains.exposed.sql.Column["table"]->org.domcek.dto.Page["columns"]....

I use jackson in my KTOR aplication

myDao:

class PageDao(id: EntityID<Int>) : IntEntity(id) {
    companion object : IntEntityClass<PageDao>(Page)

    var title by Page.title
    var body by Page.body
    var parentId by Page.parentId
    var active by Page.active
    var order by Page.order
    var slug by Page.slug

    var children: List<PageDao>? = null

    fun isMyParent(pageId: Int): Boolean {
        return pageId == this.parentId
    }
}

myHandler:

suspend fun findAll(call: ApplicationCall) {
        val pages = pageRepository.getMainPages()

        call.respond(pages)
    }

Repository:

fun getMainPages(): List<PageDao> {
        return transaction {
            addLogger(StdOutSqlLogger)

            return@transaction PageDao.find {
                Page.active.eq(true)
                Page.parentId.isNull()
            }.toList()
        }
    }

Answer 1

The simplest way (IMHO) is using a DTO (data transfer object). For example (User - DAO class):

class UserJson(val name:String=""){ constructor(user: User):this(user.name) }

respond:

      get(""){
        val users = ArrayList<UserJson>()
        transaction {
            for (user in User.all())
                users.add(UserJson(user))
        }
        call.respond(users)
    }

A using JacksonView or field annotation is looked like more complicated method.