CouchDB query to get the doc with MAX timestamp - mapreduce

Question

My CouchDB document format as below and based on the price changes there can be multiple documents with same product_id & store_id
{
"_id": "6b645d3b173b4776db38eb9fe6014a4c",
"_rev": "1-86a1d9f0af09beaa38b6fbc3095f06a8",
"product_id": "6b645d3b173b4776db38eb9fe60148ab",
"store_id": "0364e82c13b66325ee86f99f53049d39",
"price": "12000",
"currency": "AUD_$",
"time": 1579000390326
}
and I need to get the latest document (by time - the timestamp) for given product_id & store_id
For this, with my current solution I have to do two queries as below;
To get the latest timestamp. This returns the latest timestamp for given product_id & store_id
"max_time_by_product_store_id": {
"reduce": "function(keys, values) {var ids = []
values.forEach(function(time) {
if (!isNaN(time)){
ids.push(time);
}
});
return Math.max.apply(Math, ids)
}",
"map": "function (doc) {emit([doc.store_id, doc.product_id], doc.time);}"
}
Based on the latest timestamp, again I query to get the document with three parameters that are store_id, product_id & time as below,
"store_product_time": {
"map": "function (doc) {
emit([doc.store_id, doc.product_id, doc.time]);
}"
}
This works perfectly for me but my problem is I need to do two DB queries to get the document and looking for a solution to fetch the document within one DB query.
In CouchDB selector also has no way to get the document by MAX value.

Answer 1

With CouchDB's /db/_find, you can descending sort the result and limit the result to one document as follows:
{
"selector": {
"_id": {
"$gt": null
}
},
"sort": [
{
"time": "desc"
}
],
"limit": 1
}
CURL
curl -H 'Content-Type: application/json' -X POST http://localhost:5984/<db>/_find -d '{"selector":{"_id":{"$gt":null}},"sort":[{"time": "desc"}],"limit": 1}'
Please note that an index must previously be created for the sort field time (see /db/_index).