Java中使用mongodb的aggregate聚合查询
首先,我们在数据库中,mongodb的聚合查询是这样写。
db.getCollection('parking_record').aggregate(
{$match : {"appId" : "2e1800b22ae70600", "leaveTime" : {"$gt" : ISODate("2017-07-12T00:00:00"), "$lt" : ISODate("2017-07-13T00:00:00")}}},
{$group : {"_id" : "$leaveMethod", "count" : {$sum : 1}}},
{$sort : {"_id" : 1}}
)
在java类中,应该怎样呢?这是我写的其中一个方法。
(首先要导入mongodb的java驱动包mongo-java-driver-3.2.2.jar)
/**
* 根据日期统计离场方式
* @param app_id 插件ID
* @param beginDate 开始日期
* @param endDate 结束日期
* @return {"ManualLeave":2,"AutoLeave":4}
* @throws Exception
*/
public String aggregateLeaveMethodByDate(String app_id, Date beginDate, Date endDate) throws Exception {
MongoCollection<Document> collection = PluginMongo.instance().getDatabase().getCollection(MongoCollectionName.PARKING_RECORD);
Document sub_match = new Document();
sub_match.put("appId", app_id);
sub_match.put("leaveTime", new Document("$gt", beginDate).append("$lt", endDate));
Document sub_group = new Document();
sub_group.put("_id", "$leaveMethod");
sub_group.put("count", new Document("$sum", 1));
Document match = new Document("$match", sub_match);
Document group = new Document("$group", sub_group);
Document sort = new Document("$sort", new Document("_id", 1));
List<Document> aggregateList = new ArrayList<Document>();
aggregateList.add(match);
aggregateList.add(group);
aggregateList.add(sort);
JSONObject ret_obj = new JSONObject();
AggregateIterable<Document> resultset = collection.aggregate(aggregateList);
MongoCursor<Document> cursor = resultset.iterator();
try {
while(cursor.hasNext()) {
Document item_doc = cursor.next();
int leaveMethod = item_doc.getInteger("_id", 0);
int count = item_doc.getInteger("count", 0);
LeaveMethodEnum leaveMethodVal = LeaveMethodEnum.fromType(leaveMethod);
ret_obj.put(leaveMethodVal.name(), count);
}
} finally {
cursor.close();
}
return ret_obj.toJSONString();
}
上面的只有matche,group等几个常用,project,limit等类似,可以参考上面的。
aggregate的相关sql知识可以参考菜鸟教程:http://www.runoob.com/mongodb/mongodb-aggregate.html