Slick 3 join query one to many relationship - database

Question

Imagine the following relation
One book consists of many chapters, a chapter belongs to exactly one book. Classical one to many relation.
I modeled it as this:
case class Book(id: Option[Long] = None, order: Long, val title: String)
class Books(tag: Tag) extends Table[Book](tag, "books")
{
def id = column[Option[Long]]("id", O.PrimaryKey, O.AutoInc)
def order = column[Long]("order")
def title = column[String]("title")
def * = (id, order, title) <> (Book.tupled, Book.unapply)
def uniqueOrder = index("order", order, unique = true)
def chapters: Query[Chapters, Chapter, Seq] = Chapters.all.filter(_.bookID === id)
}
object Books
{
lazy val all = TableQuery[Books]
val findById = Compiled {id: Rep[Long] => all.filter(_.id === id)}
def add(order: Long, title: String) = all += new Book(None, order, title)
def delete(id: Long) = all.filter(_.id === id).delete
// def withChapters(q: Query[Books, Book, Seq]) = q.join(Chapters.all).on(_.id === _.bookID)
val withChapters = for
{
(Books, Chapters) <- all join Chapters.all on (_.id === _.bookID)
} yield(Books, Chapters)
}
case class Chapter(id: Option[Long] = None, bookID: Long, order: Long, val title: String)
class Chapters(tag: Tag) extends Table[Chapter](tag, "chapters")
{
def id = column[Option[Long]]("id", O.PrimaryKey, O.AutoInc)
def bookID = column[Long]("book_id")
def order = column[Long]("order")
def title = column[String]("title")
def * = (id, bookID, order, title) <> (Chapter.tupled, Chapter.unapply)
def uniqueOrder = index("order", order, unique = true)
def bookFK = foreignKey("book_fk", bookID, Books.all)(_.id.get, onUpdate = ForeignKeyAction.Cascade, onDelete = ForeignKeyAction.Restrict)
}
object Chapters
{
lazy val all = TableQuery[Chapters]
val findById = Compiled {id: Rep[Long] => all.filter(_.id === id)}
def add(bookId: Long, order: Long, title: String) = all += new Chapter(None, bookId, order, title)
def delete(id: Long) = all.filter(_.id === id).delete
}
Now what I want to do:
I want to query all or a specific book (by id) with all their chapters
Translated to plain SQL, something like:
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
but in Slick I can't really get this whole thing to work.
What I tried:
object Books
{
//...
def withChapters(q: Query[Books, Book, Seq]) = q.join(Chapters.all).on(_.id === _.bookID)
}
as well as:
object Books
{
//...
val withChapters = for
{
(Books, Chapters) <- all join Chapters.all on (_.id === _.bookID)
} yield(Books, Chapters)
}
but to no avail. (I use ScalaTest and I get an empty result (for def withChapters(...)) or another exception for the val withChapters = for...)
How to go on about this? I tried to keep to the documentation, but I'm doing something wrong obviously.
Also: Is there an easy way to see the actual query as a String? I only found query.selectStatement and the like, but that's not available for my joined query. Would be great for debugging to see if the actual query was wrong.
edit: My test looks like this:
class BookWithChapters extends FlatSpec with Matchers with ScalaFutures with BeforeAndAfter
{
val db = Database.forConfig("db.test.h2")
private val books = Books.all
private val chapters = Chapters.all
before { db.run(setup) }
after {db.run(tearDown)}
val setup = DBIO.seq(
(books.schema).create,
(chapters.schema).create
)
val tearDown = DBIO.seq(
(books.schema).drop,
(chapters.schema).drop
)
"Books" should "consist of chapters" in
{
db.run(
DBIO.seq
(
Books.add(0, "Book #1"),
Chapters.add(0, 0, "Chapter #1")
)
)
//whenReady(db.run(Books.withChapters(books).result)) {
whenReady(db.run(Books.withChapters(1).result)) {
result => {
// result should have length 1
print(result(0)._1)
}
}
}
}
like this I get an IndexOutOfBoundsException.
I used this as my method:
object Books
{
def withChapters(id: Long) = Books.all.filter(_.id === id) join Chapters.all on (_.id === _.bookID)
}
also:
logback.xml looks like this:
<configuration>
<logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG/>
</configuration>
Where can I see the logs? Or what else do I have to do to see them?

Answer 1

To translate your query...
SELECT * FROM books b JOIN chapters c ON books.id == c.book_id WHERE books.id = 10
...to Slick we can filter the books:
val bookTenChapters =
Books.all.filter(_.id === 10L) join Chapters.all on (_.id === _.bookID)
This will give you a query that returns Seq[(Books, Chapters)]. If you want to select different books, you can use a different filter expression.
Alternatively, you may prefer to filter on the join:
val everything =
Books.all join Chapters.all on (_.id === _.bookID)
val bookTenChapters =
everything.filter { case (book, chapter) => book.id === 10L }
That will probably be closer to your join. Check the SQL generated with the database you use to see which you prefer.
You can log the query by creating a src/main/resources/logback.xml file and set:
<logger name="slick.jdbc.JdbcBackend.statement" level="DEBUG"/>
I have an example project with logging set up. You will need to change INFO to DEBUG in the xml file in, e.g., the chapter-01 folder.