How to single value object list to array with N1QL - couchbase

Question

I have json documents in Couchbase bucket that looks like this
{
"id":"10"
"threadId": "thread1",
"createdDate": 1553285245575,
}
{
"id":"11"
"threadId": "thread1",
"createdDate": 1553285245776,
}
{
"id":"12"
"threadId": "thread2",
"createdDate": 1553285245575,
}
I'm trying to create a query that fetches documents based on group by threadId and most recent document by createdDate.
I wrote a n1ql query like this but it is only return documentId like this.
SELECT max([mes.createdDate,meta(mes).id])
from `messages` as mes
group by mes.threadId
result:
[
{
"$1": [
1553285245776,
"11"
]
},
{
"$1": [
1553285245737,
"12"
]
}
]
But i want to result like this
[{
"id":"10"
"threadId": "thread1",
"createdDate": 1553285245575,
}
{
"id":"11"
"threadId": "thread1",
"createdDate": 1553285245776,
}]
Any help would be appreciated

Answer 1

SELECT m.*
FROM `messages` AS mes
WHERE mes.threadId IS NOT NULL
GROUP BY mes.threadId
LETTING m = MAX([mes.createdDate, mes])[1];
You can use following index and query which uses covering avoids fetch.
CREATE INDEX ix1 ON `messages`(threadId, createdDate DESC, id);
SELECT m.*
FROM `messages` AS mes
WHERE mes.threadId IS NOT NULL
GROUP BY mes.threadId
LETTING m = MAX([mes.createdDate,{mes.threadId,mes.createdDate, mes.id}])[1];