Mongodb Mongo中带聚合的嵌套查询
我在MongoDB中有一个文档:Mongodb Mongo中带聚合的嵌套查询,mongodb,database,Mongodb,Database,我在MongoDB中有一个文档: { "_id" : ObjectId("111111111111111111111111"), "taskName" : "scan", "nMapRun" : { ... "hosts" : { ... "distance" : {
{
"_id" : ObjectId("111111111111111111111111"),
"taskName" : "scan",
"nMapRun" : {
...
"hosts" : {
...
"distance" : {
"value" : "1"
},..
}
我对以下字段感兴趣:nMapRun.hosts.distance.value
如何获得十个最大值这场比赛的最后一场。
您能举一个Java的例子吗?shell中的聚合操作:
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}}
])
您需要为每个阶段构建相应的DBObjects
,如下所示:
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 );
管道运行:
List<DBObject> pipeline = Arrays.asList(sort, limit, group, project);
AggregationOutput output = coll.aggregate(pipeline);
output.results().forEach(i -> System.out.println(i));
List pipeline=Arrays.asList(排序、限制、组、项目);
AggregationOutput输出=集合聚合(管道);
output.results().forEach(i->System.out.println(i));