MongoDB的聚合查询

MongoDB的聚合查询

 Java代码    

MongoClient mongoClient = null;  

try {  

    mongoClient = new MongoClient("102.198.119.29", 27017);  

    DB db = mongoClient.getDB("syslog");  

    //设置Where条件  

    DBObject match = new BasicDBObject("$match", new BasicDBObject(  

            "DATE",  

            (new BasicDBObject("$gt", "2012-11-28 00:19:00")).append(  

                    "$lt", "2012-11-29 09:19:00")));  

 

    //设置分组字段  

    BasicDBObject groupFilters = new BasicDBObject("_id", "$PRIORITY");  

    //对分组字段统计行数  

    groupFilters.put("count", new BasicDBObject("$sum", 1));  

    BasicDBObject group = new BasicDBObject("$group", groupFilters);  

    //设置显示的字段集合  

 

    DBObject fields = new BasicDBObject("PRIORITY", 1);  

    fields.put("_id", "$PRIORITY");  

    DBObject project = new BasicDBObject("$project", fields);  

    AggregationOutput output = db.getCollection("messages").aggregate(  

            match, project, group);  

    System.out.println(output.getCommandResult());  

} catch (UnknownHostException e) {  

    e.printStackTrace();  

}