Select records where id does not equal to x - kotlin

Question

I have these tables
object BooksAuthors : Table(name = "books_authors") {
val book = reference("book_id", Books, onDelete = ReferenceOption.CASCADE)
val author = reference("author_id", Authors, onDelete = ReferenceOption.CASCADE)
}
object Books : IntIdTable() {
val title = varchar("title", 250)
val isbn = varchar("isbn", 13)
}
object Authors : IntIdTable() {
val email = varchar("email", 100).uniqueIndex()
}
i would like to write a query that returns all books that dont have a specific author so i wrote this
suspend fun getBooksWithoutAuthorId(authorId: Int): List<BookDTO> = DbFactory.dbQuery {
val query = BooksAuthors.innerJoin(Books).select { BooksAuthors.author neq authorId }
Book.wrapRows(query).map { it.toDTO() }
}
But the query returns books that have the author. What am i doing wrong?

Answer 1

As Sebastian Redl mentioned, there could be books with multiple authors and your query doesn't cover that case.
Correct Exposed query should be:
val query = Books.select {
Books.id notInSubQuery
BooksAuthors.slice(BooksAuthors.book).select { BooksAuthors.author eq authorId }
}

Answer 2

It looks like you have an n:m mapping where a book can have multiple authors.
Your query, as written, finds any book that an author other than your selected one has authored.
This means if authors Alice and Bob wrote a book together, and you want to find books "not by Bob", you would still find the book because Alice took part.
Your desired query cannot be expressed as a simple join; you need nested queries instead.
Something like equivalent to this SQL:
SELECT * from books b WHERE ? NOT IN (
SELECT ab.author_id FROM authors_books ab WHERE ab.book_id = b.id);
Though I'm afraid I don't know how to express this in Exposed.
https://www.db-fiddle.com/f/7BsVUW95g6L4rXDBCoaXK3/0