在Java中实现MongoDB的Group功能

在非关系型数据库MongoDB中，并没有任何现成的框架可以像SQL那样通过GroupBy就轻松实现数据库的分组功能。如果我们想要实现MongoDB的Group功能，就必须写原生态

接口方法如下：

/** * keyColumn : new String[]{"xxxName","xxxType"}
* condition : 查询条件 ，，可为空
* initial : 分组统计初始变量，为空时自动为每列提供初始变量
* reduce ： 记录处理function
* finalize : finalize函数，可为空
*/ public BasicDBList group(String[] keyColumn, DBObject condition, DBObject initial, String reduce, String finalize) { DBCollection coll = getCollection(); DBObject key = new BasicDBObject(); for (int i = 0; i < keyColumn.length; i++) { key.put(keyColumn[i], true); } condition = (condition == null) ? new BasicDBObject() : condition; if (StringUtils.isEmpty(finalize)) { finalize = null; } if (initial == null) { //定义一些初始变量 initial = new BasicDBObject(); for (int i = 0; i < keyColumn.length; i++) { DBObject index = new BasicDBObject(); index.put("count", 0); index.put("sum", 0); index.put("max", 0); index.put("min", 0); index.put("avg", 0); index.put("self", ""); initial.put(keyColumn[i], index); } } BasicDBList resultList = (BasicDBList) coll.group(key, condition, initial, reduce, finalize); return resultList; }

实现案例：

//任务统计 @Action(value = "getTaskStatistic", results = { @Result(name = "success", type = "json", params = { "includeProperties", "jsonResult" }) }) public String getTaskStatistic() { DBObject initial = new BasicDBObject(); DBObject index = new BasicDBObject(); index.put("count", 0); index.put("taskStatus", ""); initial.put("taskStatus", index); String reduce = "function (doc, out) { " + " out.taskStatus.count = out.taskStatus.count+=1; " + " out.taskStatus.inspectStatus = doc.taskStatus;" + "}"; BasicDBList group = (BasicDBList) taskStatusService.group(new String[] { "taskStatus"}, null, initial, reduce, null); this.jsonResult = group.toString(); return SUCCESS; }

返回数据：

[ { "taskStatus" : { "count" : 4.0 , "taskStatus" : "Finished"}} , { "taskStatus" : { "count" : 3.0 , "taskStatus" : "Received"}} , { "taskStatus" : { "count" : 2.0 , "taskStatus" : "UnReceive"}}]

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