group分組統計是資料庫比較常用的功能，mongodb也不例外。不過相對於普通的增刪改查，group操作就略微麻煩一些，這裡對group在shell中的操作、使用java原生程式碼操作以及整合spring進行操作進行一個簡單的歸納總結，分組的途徑和方法應該都有多種，這裡每一樣只舉一例。本例中資料來源如下：
需要使用group實現的目的是：按年齡分組統計出每一組的數量。1、mongo shell中執行如下命令：

db.test.group({
    key:{"age":1},
    initial:{"count":0},
   $reduce:function(doc,out){ out.count++; } ,
   $finalize:function(out){ return out; }
 }
 )

執行程式碼及結果如圖：

2、java原生程式碼進行上述操作：

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);
            }
        }
    }
}
 

執行結果如圖：
3、整合spring後的操作：dao方法實現程式碼：

  /**
     * mongodb簡單分組查詢
     * 
     * @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;
    }
 

對應的實體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測試方法：

@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);
            }
        }
    }

執行結果如圖：