Scala future with unknown loop count - scala

Question

The case is try to get children comment list for a comment, and it is easy to get all the children comments by a 'parentId' field in database. However, take the possible long list into consideration, it's better to do pagination for db query. We can get specified rows like this:
def getChildCommentsByParentId(parentId: Int, offset: Int, rows: Int): Future[Seq[CommentsRow]] = {
val query = Comments.filter(row => row.iparentid === parentId && row.istatus === statusNormal ).drop(offset).take(rows)
db.run(query.result)
}
For getting all the rows by doing several pagination call with a fixed page size, it's easy to express this in an iterative way in other programing language, like this:
$replyList = [];
do {
$ret = getChildCommentsByParentId(parentId, page * pagesize, pagesize);
if (!empty($ret)) {
$replyList = array_merge($replyList, $ret);
}
if (count($ret) < $pageSize) {
break;
}
$page ++ ;
} while(true);
It's reasonable to use for comprehension to handle multiple futures in scala, but i don't know how to handle this case. The key point is, current iteration depends on previous one(the 'page' parameter), and when the count of rows is less than pagesize, returns a full result with all the previous data rows.
Thanks!

Answer 1

I try to solve it in a recursive way:
def getChildComments(nextPage: Int, commentId: Int) : Future[CommentResult] = {
val pageSize = 5
val currentPageFuture = commentModel.getChildCommentsByParentId(commentId, nextPage*pageSize, pageSize).map {
data => CommentResult(nextPage, data)
}
val nextPageFuture = currentPageFuture.flatMap({ commentRes =>
val nextPage = commentRes.nextPage+1
if(commentRes.data.size >= pageSize) {
getChildComments(nextPage, commentId)
}
else {
Future.successful(CommentResult(nextPage, Seq()))
}
})
for {
currentPageComments <- currentPageFuture
nextPageComments <- nextPageFuture
} yield {
CommentResult(currentPageComments.nextPage, currentPageComments.data ++ nextPageComments.data)
}
}
case class CommentResult(nextPage: Int, data: Seq[TbcommentsRow])
But still feel it's ugly, doubt it has more elegant way?