Eager loading

I have the following code.

class Author(id: EntityID<Int>): IntEntity(id){
    companion object : IntEntityClass<Author>(Authors)

    var firstName by Authors.firstName
    var lastName by Authors.lastName
    override fun toString(): String {
        return "Author($id, $firstName, $lastName)"
    }
}

object Authors: IntIdTable(){
    val firstName = varchar("firstName", 50)
    val lastName = varchar("lastName", 50)
}

class Book(id: EntityID<Int>): IntEntity(id){
    companion object : IntEntityClass<Book>(Books)

    var name by Books.name
    var authors by Author via BookAuthors
    override fun toString(): String {
        return "Book($id, $name, authors: [$authors])"
    }
}

object Books: IntIdTable(){
    val name = varchar("name", 50)
}

object BookAuthors: Table() {
    val book = reference("book", Books).primaryKey(0)
    val author = reference("author", Authors).primaryKey(1)
}

Studing documentation I can add new Book and Author

val book = transaction {
	Book.new {
		name = "test book"
	}
}
val author = transaction {
	 Author.new {
		firstName = "FName"
		lastName = "LName"
	}
}

as well as create reference

transaction {
	 book.authors = SizedCollection(listOf(author))
}

The problem I have is that after getting all books with eager loading, collection is not printed as expected

for (bookItem in Book.all().with(Book::authors)) {
	println(bookItem)
}

Reult Book(1, test book, authors: [org.jetbrains.exposed.sql.LazySizedCollection@7c56e013])

val book1 = Book.findById(1)?.load(Book::authors)
println(book1)
//same result 
//Book(1, test book, authors: [org.jetbrains.exposed.sql.LazySizedCollection@7c56e013])

println(book1?.authors)
//authors not printed 
//org.jetbrains.exposed.sql.LazySizedCollection@7c56e013

println(book1?.authors?.with(Book::authors))
//now it can print authors? 
//[Author(1, FName, LName)]

println(book1)
//still same issue 
//Book(1, test book, authors: [org.jetbrains.exposed.sql.LazySizedCollection@7c56e013])

Could you help with that? What might be the problem? My assumption is that Book.findById(1)?.load(Book::authors) is not loading, am I correct?

Console debugg logs shows that authors are selected, but they are not populated in Book.all() DEBUG Exposed - SELECT AUTHORS.ID, AUTHORS."firstName", AUTHORS."lastName", BOOKAUTHORS.AUTHOR, BOOKAUTHORS.BOOK FROM AUTHORS INNER JOIN BOOKAUTHORS ON BOOKAUTHORS.AUTHOR = AUTHORS.ID WHERE BOOKAUTHORS.BOOK IN (1, 2)

[uuf6429]

All transformations that use the eager loaded relations have to be done inside the transaction closure, as relations are stored inside the cache for that specific transaction. This is just a limitation of the feature unfortunately. In short in your example above your println would need to go inside the transaction closure

@CharlieTap I have this same issue and unfortunately, it’s not clear why this problem happens. If the object graph is loaded eagerly in a transaction, why is another (or same) transaction needed again later on? Also, perhaps the point of eager loading is not very clear. cc @Tapac

[CharlieTap]

All transformations that use the eager loaded relations have to be done inside the transaction closure, as relations are stored inside the cache for that specific transaction. This is just a limitation of the feature unfortunately. In short in your example above your println would need to go inside the transaction closure