Join three tables in Scala Slick or flatten nested tuples - scala

Question

I need to do INNER JOIN three tables because of foreign key in the first one as follows:
CREATE TABLE "product" (
"id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
"name" VARCHAR NOT NULL,
"price" FLOAT NOT NULL,
"categoryid" INT NOT NULL,
"supplierid" INT NOT NULL,
FOREIGN KEY(categoryid) references category(id),
FOREIGN KEY(supplierid) references supplier(id)
);
In models I have method to handle list all:
def list(): Future[Seq[(Product, Category, Supplier)]] = db.run {
productTable.join(categoryTable).on(_.categoryid === _.id).join(supplierTable).on(_._1.supplierid === _.id).result
}
But this returns nested tuple instead of flat one: ((Product, Category), Supplier).
Then how should I join those tables to get flat tuple or, if not possible to do that, how can I flatten this tuple?
EDIT:
Actually the only solution I found which works for me is manual use of map:
def list(): Future[Seq[(Product, Category, Supplier)]] = db.run {
productTable.join(categoryTable).on(_.categoryid === _.id).join(supplierTable).on(_._1.supplierid === _.id).result.map(a => Seq((a(1)._1._1,a(1)._1._2,a(1)._2)))
}
Which looks and feels horrible. But only this works so far ...
Any better ideas?

Answer 1

Inner joins are expressed as for comprehensions in Slick:
def list(): Future[Seq[(Product, Category, Supplier)]] = db.run {
for {
product <- productTable
category <- categoryTable if product.categoryid === category.id
supplier <- supplierTable if product.supplierid === supplier.id
} yield (product, category, supplier)
}
I would also recommend you to check out Slick's support for foreign key queries. That would make the query quite a bit simpler, it would probably look something like this:
def list(): Future[Seq[(Product, Category, Supplier)]] = db.run {
for {
product <- productTable
category <- product.category
supplier <- product.supplier
} yield (product, category, supplier)
}