怎么在java中获得mongodb分组group的结果中的总数量

发布网友发布时间：2022-05-01 07:15

共3个回答

懂视网时间：2022-05-01 11:36

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：技术分享

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：
环境搭建可参考：http://blog.csdn.net/tuzongxun/article/details/51404529
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：

mongodb命令行group分组和java代码中group分组

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热心网友时间：2022-05-01 08:44

用.count()方法获取总数，可以直接在group中获取。

热心网友时间：2022-05-01 10:02

java中直接将结果映射成POJO,然后获取其属性即可。