在Java中实现MongoDB的Group功能

文章由LinuxBoy分享于2019-03-30 04:03:32热评（412）

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：
/**
* 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"}}]

MongoDB 的详细介绍：请点这里
MongoDB 的下载地址：请点这里

在Java中实现MongoDB的Group功能