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：

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/**
* 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：

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//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"}}]

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