最近專案用mongdb，作為資料庫。要實現抽獎專案，按照收集卡片的多少來排名，顯示前15名的使用者中獎資訊。

cllection 名稱： wzl_app_winnerlist  每次收集一張卡片都會有一條記錄。

使用自帶的命令列客戶端聚合語句： 

db.getCollection('wzl_app_winnerlist').aggregate([
    {$match:{'times':'1'}},
    {$group:{'_id'
    :{'times':'$times','user_id':'$user_id','user_account':'$user_account'},'count':{$sum:1}}},
    {$sort:{'count':-1}},
    {$limit:15},
    {$project:{'_id':0,'times':'$_id.times','user_id':'$_id.user_id','user_account':'$_id.user_account','count':1}}
    ]);

其中times,為活動期次，user_id ,為使用者id,user_accout,為使用者名稱, count 為統計數量。

$match:過濾條件

$group:分組 按照_id 分組,並查詢出資料。

$sort: 排序,按照count 降序排列。

$limit: 限制數量

$project: 聚合，0 不顯示，1顯示。

最後結果

[
    {
        "count": 31,
        "times": "1",
        "user_id": "20",
        "user_account": "17812345678"
    },
    {
        "count": 29,
        "times": "1",
        "user_id": "7",
        "user_account": "18123456789"
    },
    {
        "count": 23,
        "times": "1",
        "user_id": "1",
        "user_account": "13524354057"
    },
    {
        "count": 22,
        "times": "1",
        "user_id": "4",
        "user_account": "13412345678"
    },
    {
        "count": 20,
        "times": "1",
        "user_id": "11",
        "user_account": "22222222222"
    },
    {
        "count": 20,
        "times": "1",
        "user_id": "5",
        "user_account": "15026994613"
    },
    {
        "count": 17,
        "times": "1",
        "user_id": "16",
        "user_account": "19193840921"
    },
    {
        "count": 16,
        "times": "1",
        "user_id": "2",
        "user_account": "13333333333"
    },
    {
        "count": 16,
        "times": "1",
        "user_id": "10",
        "user_account": "18412345678"
    },
    {
        "count": 16,
        "times": "1",
        "user_id": "9",
        "user_account": "18312345678"
    },
    {
        "count": 15,
        "times": "1",
        "user_id": "13",
        "user_account": "18012345678"
    },
    {
        "count": 14,
        "times": "1",
        "user_id": "12",
        "user_account": "33333333333"
    },
    {
        "count": 14,
        "times": "1",
        "user_id": "19",
        "user_account": "12345678909"
    },
    {
        "count": 13,
        "times": "1",
        "user_id": "14",
        "user_account": "18123456783"
    },
    {
        "count": 13,
        "times": "1",
        "user_id": "17",
        "user_account": "13234242343"
    }
]

java driver 驅動聚合函式操作：

實現以上效果：

	  public static String queryWinners(HttpServletRequest request,HttpServletResponse response,JsonNode node,String sUserID) throws Exception {


		  String times  = Util.getValue(node, "times") ;
		  String limitStr =  Util.getValue(node, "limit") ;
		  int limit = -1 ;
		  if (limitStr!=null&&!"".equals(limitStr)) {
			  limit  = Integer.parseInt(limitStr) ;
		  }else {
			limit = 10 ;
		  }
		  
		  if (times==null||"".equals(times)) {
			 return "{s:1,m:請求引數錯誤}";
		  }
		  //根據期次和使用者id 查詢  使用者id 分組,limit 15 .
		  DBCollection collection = DBUtil.getCollection(Constant.WZL_APP_WINNERLIST);
		  DBObject matchBasicDBObjet = new BasicDBObject("$match",new BasicDBObject("times",times));
		  /* Group操作*/
		  DBObject groupFields = new BasicDBObject("_id", new BasicDBObject("times", "$times").append("user_id", "$user_id").append("user_account", "$user_account"));
		  groupFields.put("count", new BasicDBObject("$sum", 1));
		  DBObject group = new BasicDBObject("$group", groupFields);
		  
		  // 排序操作
		  DBObject sortchBasicDBObjet = new BasicDBObject("$sort", new BasicDBObject("count",-1));
		  DBObject limitBasicDBObjet = new BasicDBObject("$limit",limit);
		  // project 操作
		  DBObject projectBasicDBObjet = new BasicDBObject("$project",
				  new BasicDBObject("_id",0).append("times", "$_id.times")
				  .append("user_id", "$_id.user_id").append("user_account", "$_id.user_account").append("count", 1));
		
		  List<DBObject> list = new ArrayList<DBObject>();
		  list.add(matchBasicDBObjet);
		  list.add(group);
		  list.add(sortchBasicDBObjet);
		  list.add(limitBasicDBObjet);
		  list.add(projectBasicDBObjet);
		  
		  AggregationOutput output = collection.aggregate(list);
		CommandResult result = output.getCommandResult();
		//方案二
//		 JsonNode resultnode = JsonUtil.getJson(result.getString("result"));
//		  logger.info(JsonMapper.toJsonString(resultnode)); 
		
		  logger.info(result.getString("result"));


		  return result.getString("result");
	}