group分组统计是数据库比较常用的功能，mongodb也不例外。不过相对于普通的增删改查，group操作就略微麻烦一些，
这里对group在shell中的操作、使用java原生代码操作以及集成spring进行操作进行一个简单的归纳总结，分组的途径和方法应该都有多种，这里每一样只举一例。
本例中数据源如下：
需要使用group实现的目的是：按年龄分组统计出每一组的数量。
1、mongo shell中执行如下命令：
db.test.group({
key:{"age":1},
initial:{"count":0},
$reduce:function(doc,out){ out.count++; } ,
$finalize:function(out){ return out; }
}
)
执行代码及结果如图：
2、java原生代码进行上述操作：
public class MonTest {
public static void main(String[] args) {
monGroup();
}
public static void monGroup() {
ServerAddress sa = new ServerAddress("192.168.0.201", 37017);
List<MongoCredential> mongoCredentialList = new ArrayList<MongoCredential>();
mongoCredentialList.add(MongoCredential.createMongoCRCredential("admin", "admin", "123456".toCharArray()));
Mongo client = new MongoClient(sa, mongoCredentialList);
DB database = client.getDB("admin");
DBCollection coll = database.getCollection("test");
DBObject keys = new BasicDBObject("age", 1);
DBObject condition = null;
DBObject initial = new BasicDBObject("count", 0);
String reduce = "function(doc,out){out.count++;}";
String finalize = "function(out){return out;}";
BasicDBList dbList = (BasicDBList) coll.group(keys, condition, initial, reduce, finalize);
if (dbList != null) {
for (int i = 0; i < dbList.size(); i++) {
DBObject obj = (DBObject) dbList.get(i);
Object age = obj.get("age");
Object count = obj.get("count");
System.out.println("age:" + age + ",count:" + count);
}
}
}
}
执行结果如图：
3、集成spring后的操作：
dao方法实现代码：
/**
* mongodb简单分组查询
*
* @author：tuzongxun
* @Title: mongoGroup
* @param @return
* @date Jul 19, 2016 8:36:19 AM
* @throws
*/
@Override
public BasicDBList mongoGroup() {
// TODO Auto-generated method stub
GroupBy groupBy = GroupBy.key("age").initialDocument("{count:0}").reduceFunction("function(doc, out){out.count++}")
.finalizeFunction("function(out){return out;}");
GroupByResults<UserModel> res = mongoTemplate.group("test", groupBy, UserModel.class);
DBObject obj = res.getRawResults();
BasicDBList dbList = (BasicDBList) obj.get("retval");
return dbList;
}
对应的实体model：
package spring_mongo.models;
import java.io.Serializable;
public class UserModel implements Serializable {
private static final long serialVersionUID = 1L;
private String name;
private int age;
public UserModel(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "UserModel [name=" + name + ", age=" + age + "]";
}
}
junit测试方法：
@Test
public void mongoGroup() {
BasicDBList dbList = userDao.mongoGroup();
if (dbList != null) {
for (int i = 0; i < dbList.size(); i++) {
DBObject obj = (DBObject) dbList.get(i);
Object age = obj.get("age");
Object count = obj.get("count");
System.out.println("age:" + age + ",count:" + count);
}
}
}
运行结果如图：