mongo aggregation

在mongo中 aggregation（聚合应用）

1、插入测试数据

db.tycoon.insertMany( [
   {item:"paper",tycoon:25,size:{h:14, w:21,cm:"and" },status:"A"},
   {item:"notebook",tycoon:50,size:{h:8.5, w:11,cm:"in" },status:"B"},
   {item:"pencil",tycoon:100,size:{h:8.5, w:11,cm:"max" },status:"C"},
   {item:"schoolbag",tycoon:75,size:{h:1.85, w:30,cm:"avg" },status:"D"},
   {item:"ruler",tycoon:45,size:{h:10, w:15.25,cm:"count" },status:"E"}]);

2、java 测试

Aggregation aggregation =
    Aggregation.newAggregation(
        Aggregation.match(Criteria.where("size.h").gte(9.0)),
        Aggregation.unwind("size"),
        Aggregation.group("$size.cm").avg("$size.w").as("平均").min("$size.w").as
      ("MinValue").max("$size.w").as("MaxValue").sum("$size.w").as("SumItem"));
        AggregationResults<BasicDBObject> result=
                template.aggregate(aggregation, "tycoon", BasicDBObject.class);
      for (Iterator<BasicDBObject> iterator = result.iterator(); iterator.hasNext(); ) {
            DBObject obj = iterator.next();
            System.out.println(obj);
        }
    }