Scala Slick 3.0.1 Relationship to self - scala

Question

I have an entity called Category which has a relationship to itself. There are two types of categories, a parent category and a subcategory. The subcategories have in the idParent attribute, the id from the parent category.
I defined the Schema this way
class CategoriesTable(tag: Tag) extends Table[Category](tag, "CATEGORIES") {
def id = column[String]("id", O.PrimaryKey)
def name = column[String]("name")
def idParent = column[Option[String]]("idParent")
def * = (id, name, idParent) <> (Category.tupled, Category.unapply)
def categoryFK = foreignKey("category_fk", idParent, categories)(_.id.?)
def subcategories = TableQuery[CategoriesTable].filter(_.id === idParent)
}
And I have this data:
id name idParent
------------------------------
parent Parent
child1 Child1 parent
child2 Child2 parent
Now I want to get the result in a map grouped by the parent category like
Map(
(parent,Parent,None) -> Seq[(child1,Child1,parent),(child2,Child2,parent]
)
For that I tried with the following query:
def findChildrenWithParents() = {
db.run((for {
c <- categories
s <- c.subcategories
} yield (c,s)).sortBy(_._1.name).result)
}
If at this point I execute the query with:
categoryDao.findChildrenWithParents().map {
case categoryTuples => categoryTuples.map(println _)
}
I get this:
(Category(child1,Child1,Some(parent)),Category(parent,Parent,None))
(Category(child2,Child2,Some(parent)),Category(parent,Parent,None))
Here there are two facts that already disconcerted me:
It is returning Future[Seq[Category, Category]] instead of the Future[Seq[Category, Seq[Category]]] that I would expect.
The order is inverted, I would expect the parent to appear first like:
(Category(parent,Parent,None),Category(child1,Child1,Some(parent)))
(Category(parent,Parent,None),Category(child2,Child2,Some(parent)))
Now I would try to group them. As I am having problems with nested queries in Slick. I perform a group by on the result like this:
categoryDao.findChildrenWithParents().map {
case categoryTuples => categoryTuples.groupBy(_._2).map(println _)
}
But the result is really a mess:
(Category(parent,Parent,None),Vector((Category(child1,Child1,Some(parent)),Category(parent,Parent,None),(Category(child2,Child2,Some(parent)),Category(parent,Parent,None))))
I would have expected:
(Category(parent,Parent,None),Vector(Category(child1,Child1,Some(parent)),Category(child2,Child2,Some(parent))))
Can you please help me with the inverted result and with the group by?
Thanks in advance.

Answer 1

Ok I managed to fix it by myself. Here the answer if someone wants to learn from it:
def findChildrenWithParents() = {
val result = db.run((for {
c <- categories
s <- c.subcategories
} yield (c,s)).sortBy(_._1.name).result)
result map {
case categoryTuples => categoryTuples.groupBy(_._1).map{
case (k,v) => (k,v.map(_._2))
}
}
}
The solution isn't perfect. I would like to make the group by already in Slick, but this retrieves what I wanted.