I have a document in MongoDB:
{
"_id" : ObjectId("111111111111111111111111"),
"taskName" : "scan",
"nMapRun" : {
...
"hosts" : {
...
"distance" : {
"value" : "1"
},..
}
I'm interested in the field: nMapRun.hosts.distance.value How do I get ten maximum values of the field . Could you give an example of a Java?
The aggregation operation in shell:
db.collection.aggregate([
{$sort:{"nMapRun.hosts.distance.value":-1}},
{$limit:10},
{$group:{"_id":null,"values":{$push:"$nMapRun.hosts.distance.value"}}},
{$project:{"_id":0,"values":1}}
])
You need to build the corresponding DBObjects for each stage as below:
DBObject sort = new BasicDBObject("$sort",
new BasicDBObject("nMapRun.hosts.distance.value", -1));
DBObject limit = new BasicDBObject("$limit", 10);
DBObject groupFields = new BasicDBObject( "_id", null);
groupFields.put("values",
new BasicDBObject( "$push","$nMapRun.hosts.distance.value"));
DBObject group = new BasicDBObject("$group", groupFields);
DBObject fields = new BasicDBObject("values", 1);
fields.put("_id", 0);
DBObject project = new BasicDBObject("$project", fields );
Running the aggregation pipeline:
List<DBObject> pipeline = Arrays.asList(sort, limit, group, project);
AggregationOutput output = coll.aggregate(pipeline);
output.results().forEach(i -> System.out.println(i));
