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Group By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，就必须写原生态的NO-SQL 查询语句来实现Group功能，这样既费时又费力，而且很容易出错，本文提供了一个封装的接口来实现MongoDB的Group功能，让程序员从此不再为MongoDB的Group而发愁。

　　接口方法如下：

1234567891011121314151617181920212223242526272829303132333435/** * keyColumn : new String[]{"xxxName","xxxType"} <br> * condition : 查询条件 ，可为空<br> * initial : 分组统计初始变量，为空时自动为每列提供初始变量<br> * reduce ： 记录处理function<br> * finalize : finalize函数，可为空 <br> */ 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：

12345678910111213141516171819//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：

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

1楼lfmilaoshi13分钟前

我最近是在使用非结构化数据库，还是在研究非结构化数据库？