Scala Slick 3: Count Rows and get row - sql

Question

I cannot figure out how to count with Slick (3).
val posts = for {
p <- Posts.query if p.receiver === userId
comments <- Comments.query if comments.postId === p.id
author <- Users.query if p.author === author.id
receiver <- Users.query if p.receiver === receiver.id
} yield (p, comments, author, receiver)
With the following relationships
Posts : Author : Receiver : Comments
1 : 1 : 1 : N
The result should be:
Future[Seq[(Post, User, User, Int)]]
with the int being the count of comments grouped by Posts
Any tips?

Answer 1

You need to group your result by post, author and receiver and the map to aggregate the comments by just counting them.
val posts = (for {
p <- Posts.query if p.receiver === userId
comment <- Comments.query if comments.postId === p.id
author <- Users.query if p.author === author.id
receiver <- Users.query if p.receiver === receiver.id
} yield (p, comment, author, receiver)) //So far thats your current query
.groupBy({ //Group by post, author and receiver
case (post, comment, author, receiver) =>
(post, author, receiver)
})
.map({ //Aggregate your comments (second argument in tuple) and count them
case ((post, author, receiver), list) => {
(post, author, receiver, list.map(_._2).count))
}
})
On mobile currently so this probably won't compile, but you should get the idea.