Hibernate之检索单个对象

Query和Criteria接口都提供执行查询语句，并且返回查询结果的方法，返回结果有两种类型，在先前的学习中，

使用的都是返回list,输出结果还得循环，有时候我们只想查询一条数据，没有必要让查询结果返回一个集合，

这个时候，返回一个对象就好。

针对返回集合，Query和Criteria提供list()方法，集合中存放满足条件的持久化对象。

针对返回单个对象，Query和Criteria提供uniqueResult()方法，返回单个满足条件的持久化对象。

返回单个对象的逻辑：

（1）使用setMaxResults(1)设置最多检出条数

（2）使用uniqueResult()返回一个Object类型对象，再强制转换成你想要的类型

HQL检索单个对象实例：

package com.lanhuigu.hibernate.test;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.lanhuigu.hibernate.entity.Customer;

public class TestHQLUnique {
public static void main(String[] args){
Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction tr = session.beginTransaction();
//1.创建Query
Query query = session.createQuery("from Customer order by name desc ");
//2.设置最大检出条数
query.setMaxResults(1);
//3.执行sql，返回一个Object对象，强制转换为Customer对象
Customer customer = (Customer) query.uniqueResult();
//4.输出结果
System.out.println(customer.getName());
//5.事务提交
tr.commit();
//6.关闭session
session.close();
}
}

控制台输出结果：

Hibernate: select this_.ID as ID1_0_0_, this_.NAME as NAME2_0_0_, this_.EMAIL as EMAIL3_0_0_, this_.PASSWORD as PASSWORD4_0_0_, this_.PHONE as PHONE5_0_0_, this_.ADDRESS as ADDRESS6_0_0_, this_.SEX as SEX7_0_0_, this_.IS_MARRIED as IS8_0_0_, this_.DESCRIPTION as DESCRIPT9_0_0_, this_.IMAGE as IMAGE10_0_0_, this_.BIRTHDAY as BIRTHDA11_0_0_, this_.REGISTERED_TIME as REGISTE12_0_0_, this_.HOME_PROVINCE as HOME13_0_0_, this_.HOME_CITY as HOME14_0_0_, this_.HOME_STREET as HOME15_0_0_, this_.HOME_ZIPCODE as HOME16_0_0_, this_.COMP_PROVINCE as COMP17_0_0_, this_.COMP_CITY as COMP18_0_0_, this_.COMP_STREET as COMP19_0_0_, this_.COMP_ZIPCODE as COMP20_0_0_ from CUSTOMERS this_ order by this_.NAME desc limit ?
test

QBC检索单个对象实例：

package com.lanhuigu.hibernate.test;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Order;

import com.lanhuigu.hibernate.entity.Customer;

public class TestQBCUnique {
public static void main(String[] args) throws Exception{
Configuration cfg = new Configuration().configure();
SessionFactory sessionFactory = cfg.buildSessionFactory();
Session session = sessionFactory.openSession();
Transaction tr = session.beginTransaction();
//1.创建Criteria对象
Criteria criteria = session.createCriteria(Customer.class);
//2.排序
//criteria.addOrder(Order.asc("name"));//升序
criteria.addOrder(Order.desc("name"));//降序
//3.设置最大检出数据条数
criteria.setMaxResults(1);//最多检出的条数
//4.执行SQL，返回一个Object对象，强制转换为Customer对象
Customer customer = (Customer) criteria.uniqueResult();
//5.输出结果
System.out.println(customer.getName());
//6.事务提交
tr.commit();
//7.关闭session
session.close();
}
}

控制台输出结果：

Hibernate: select this_.ID as ID1_0_0_, this_.NAME as NAME2_0_0_, this_.EMAIL as EMAIL3_0_0_, this_.PASSWORD as PASSWORD4_0_0_, this_.PHONE as PHONE5_0_0_, this_.ADDRESS as ADDRESS6_0_0_, this_.SEX as SEX7_0_0_, this_.IS_MARRIED as IS8_0_0_, this_.DESCRIPTION as DESCRIPT9_0_0_, this_.IMAGE as IMAGE10_0_0_, this_.BIRTHDAY as BIRTHDA11_0_0_, this_.REGISTERED_TIME as REGISTE12_0_0_, this_.HOME_PROVINCE as HOME13_0_0_, this_.HOME_CITY as HOME14_0_0_, this_.HOME_STREET as HOME15_0_0_, this_.HOME_ZIPCODE as HOME16_0_0_, this_.COMP_PROVINCE as COMP17_0_0_, this_.COMP_CITY as COMP18_0_0_, this_.COMP_STREET as COMP19_0_0_, this_.COMP_ZIPCODE as COMP20_0_0_ from CUSTOMERS this_ order by this_.NAME desc limit ?
test