Using Spring Data Mongodb, is it possible to get the max value of a field without pulling and iterating over an entire collection?

Question

Using mongoTemplate.find(), I specify a Query with which I can call .limit() or .sort():

.limit() returns a Query object
.sort() returns a Sort object

Given this, I can say Query().limit(int).sort(), but this does not perform the desired operation, it merely sorts a limited result set.

I cannot call Query().sort().limit(int) either since .sort() returns a Sort()

So using Spring Data, how do I perform the following as shown in the mongoDB shell? Maybe there's a way to pass a raw query that I haven't found yet?

I would be ok with extending the Paging interface if need be...just doesn't seem to help any. Thanks!

> j = { order: 1 }
{ "order" : 1 }
> k = { order: 2 }
{ "order" : 2 }
> l = { order: 3 }
{ "order" : 3 }
> db.test.save(j)
> db.test.save(k)
> db.test.save(l)
> db.test.find()
{ "_id" : ObjectId("4f74d35b6f54e1f1c5850f19"), "order" : 1 }
{ "_id" : ObjectId("4f74d3606f54e1f1c5850f1a"), "order" : 2 }
{ "_id" : ObjectId("4f74d3666f54e1f1c5850f1b"), "order" : 3 }
> db.test.find().sort({ order : -1 }).limit(1)
{ "_id" : ObjectId("4f74d3666f54e1f1c5850f1b"), "order" : 3 }

Answer 1

You can do this in sping-data-mongodb. Mongo will optimize sort/limit combinations IF the sort field is indexed (or the @Id field). This produces very fast O(logN) or better results. Otherwise it is still O(N) as opposed to O(N*logN) because it will use a top-k algorithm and avoid the global sort (mongodb sort doc). This is from Mkyong's example but I do the sort first and set the limit to one second.

Query query = new Query();
query.with(new Sort(Sort.Direction.DESC, "idField"));
query.limit(1);
MyObject maxObject = mongoTemplate.findOne(query, MyObject.class);