mongodb的高级操作（聚合框架）

重点探讨mongodb  对某个字段 sum求和

new BasicDBObject("$group",new BasicDBObject("_id","$number").append("total", new BasicDBObject("$sum","$"+"length")));

new BasicDBObject("_id","$"+queryField)为固定格式

group by 查询 不要用java驱动带的group by ，要用2.2版本后的aggregate聚合框架来搞，经过试验速度快一倍

参考

官网：http://docs.mongodb.org/manual/reference/sql-aggregation-comparison/

实例：http://www.yeetrack.com/?p=649

观看例子前，请先看上面对的2个参考文档，特别是官网的

例子 

// 首先利$match筛选出where条件
BasicDBObject[] array = {
new BasicDBObject("startTimeLong", new BasicDBObject("$gte",beginTime)),
new BasicDBObject("startTimeLong", new BasicDBObject("$lt",endTime)) };

BasicDBObject cond = new BasicDBObject();
cond.put("$and", array);
DBObject match = new BasicDBObject("$match", cond);

// 利用$project拼装group需要的数据，包含optCode列、processTime列
DBObject fields = new BasicDBObject("optCode", 1); // 接口
fields.put("processTime", 1);// 耗时
fields.put("provinceCode", 1);// 省份
fields.put("channelSubCode", 1);// 渠道
fields.put("platFormCode", 1);// 平台

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

// 利用$group进行分组
DBObject _group = new BasicDBObject("provinceCode", "$provinceCode");
_group.put("channelSubCode", "$channelSubCode");
_group.put("platFormCode", "$platFormCode");
_group.put("optCode", "$optCode");

DBObject groupFields = new BasicDBObject("_id", _group);
//总数
groupFields.put("count", new BasicDBObject("$sum", 1));
//求和
groupFields.put("processTime_sum", new BasicDBObject("$sum","$processTime"));
DBObject group = new BasicDBObject("$group", groupFields);
AggregationOutput output = MongodbUtil.getLogInfoCollection().aggregate(match, project, group);

/**
* 对一个字段求和
* @param collectionName
* @param where
* @param groupFields
* @return
*/
public Double sum(String collectionName,DBObject where,String sumField){

DBCollection col=mongoDbFactory.getDb().getCollection(collectionName);
DBObject match=new BasicDBObject("$match",where);
DBObject group=new BasicDBObject("$group",new BasicDBObject("_id",null).append("total", new BasicDBObject("$sum","$"+sumField)));
List<DBObject> list=(List<DBObject>)col.aggregate(match,group).results();
if(list.size()>0){
return Double.valueOf(list.get(0).get("total").toString());
}
return 0D;
}

个人实例：查询消费总和

public long getCostCount(String number, String type, int month) {
DBCollection dbc = getCollection(Constant.MongoDBName, Constant.CostDetails);
DBObject dbObject = new BasicDBObject();
dbObject.put("number", number);
dbObject.put("type", type);
dbObject.put("month", month);

//设置Where条件
DBObject match = new BasicDBObject("$match",dbObject);
//设置分组字段
DBObject group=new BasicDBObject("$group",new BasicDBObject("_id","$number").append("total", new BasicDBObject("$sum","$"+"length")));
List<DBObject> list=(List<DBObject>)dbc.aggregate(match,group).results();
if(list != null && list.size()>0){
LOG.info(list.get(0).toString());
return Long.valueOf(list.get(0).get("total").toString());
}else{
return 0l;
}
}