4_MyBatis传统DAO模式开发-1_sqlSession查询的三种方式

喜欢ヅ旅行 2023-09-27 13:17 9阅读 0赞

普通模式,也称为传统DAO模式,就是在传统DAO模式下,定义接口和实现类,如 interface EmpDao class EmpDaoImpl implements EmpDao. 在实现类中,用SQLSession对象调用select insert delete update 等方法实现.目前极为少见.在传统模式下,我们需要知道SqlSession对象 实现CURD和 参数传递的处理

1\_sqlSession查询的三种方式

SqlSession对象本身的API中就有三个查询方法,分别能够实现如下查询方式

1返回单个对象 selectOne

2返回对象List集合 selectList

3返回对象Map集合 selectMap

接下来我们就对这三个方法进行一个快速的学习

![d8ea7a617a29a8fc2588b1f93d81c9a1.png][]

创建Emp实体类

*  @AllArgsConstructor
 *  @NoArgsConstructor
 *  @Data
 *  public class Emp implements Serializable \{
 *  private Integer empno;
 *  private String ename;
 *  private String job;
 *  private Integer mgr;
 *  private Date hiredate;
 *  private Double sal;
 *  private Double comm;
 *  private Integer deptno;
 *  
 *  \}
 *

准备Mapper映射文件

*  <?xml version="1.0" encoding="UTF-8" ?>
 *  <!DOCTYPE mapper
 *  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 *  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 *  
 *  <mapper namespace="EmpMapper">
 *  
 *  
 *  <select id="findOne" resultType="emp" >
 *  select \* from emp where empno = 7499
 *  </select>
 *  
 *  
 *  
 *  <select id="findAll" resultType="emp">
 *  select \* from emp
 *  </select>
 *  
 *  
 *  <select id="findEmpMap" resultType="map">
 *  select \* from emp
 *  </select>
 *  
 *  </mapper>
 *

sqlMapConfig中导入EmpMapper映射文件

*  
 *  <mappers>
 *  <mapper resource="com/msb/mapper/DeptMapper.xml"/>
 *  <mapper resource="com/msb/mapper/EmpMapper.xml"/>
 *  </mappers>

测试代码

*  package com.msb.test;
 *  
 *  import com.msb.pojo.Dept;
 *  import com.msb.pojo.Emp;
 *  import org.apache.ibatis.io.Resources;
 *  import org.apache.ibatis.session.SqlSession;
 *  import org.apache.ibatis.session.SqlSessionFactory;
 *  import org.apache.ibatis.session.SqlSessionFactoryBuilder;
 *  import org.junit.After;
 *  import org.junit.Before;
 *  import org.junit.Test;
 *  
 *  import java.io.IOException;
 *  import java.io.InputStream;
 *  import java.util.List;
 *  import java.util.Map;
 *  import java.util.Set;
 *  
 *  /\*\*
 *  \* @Author: Ma HaiYang
 *  \* @Description: MircoMessage:Mark\_7001
 *  \*/
 *  public class Test2 \{
 *  
 *  private SqlSession sqlSession;
 *  @Before
 *  public void init()\{
 *  SqlSessionFactoryBuilder ssfb =new SqlSessionFactoryBuilder();
 *  InputStream resourceAsStream = null;
 *  try \{
 *  resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
 *  \} catch (IOException e) \{
 *  e.printStackTrace();
 *  \}
 *  SqlSessionFactory factory=ssfb.build(resourceAsStream) ;
 *  sqlSession=factory.openSession();
 *  \}
 *  
 *  @Test
 *  public void testSelectOne()\{
 *  // 查询单个对象
 *  System.out.println("sqlSession查询单个对象");
 *  Emp emp = sqlSession.selectOne("findOne");
 *  System.out.println(emp);
 *  
 *  \}
 *  
 *  @Test
 *  public void testSelectList()\{
 *  // 查询多个对象的List集合
 *  System.out.println("sqlSession查询对象List集合");
 *  List<Emp> emps = sqlSession.selectList("EmpMapper.findAll");
 *  emps.forEach(System.out::println);
 *  \}
 *  
 *  @Test
 *  public void testSelectMap()\{
 *  // 查询多个对象的Map集合
 *  System.out.println("sqlSession查询对象Map集合");
 *  Map<Integer, Emp> empMap = sqlSession.selectMap("findEmpMap", "EMPNO");
 *  Set<Integer> empnos = empMap.keySet();
 *  for (Integer empno : empnos) \{
 *  System.out.println(empno+" :" +empMap.get(empno));
 *  \}
 *  \}
 *  
 *  @After
 *  public void release()\{
 *  // 关闭SQLSession
 *  sqlSession.close();
 *  \}
 *  
 *  \}
 *  
 *

[d8ea7a617a29a8fc2588b1f93d81c9a1.png]: https://img-blog.csdnimg.cn/img_convert/d8ea7a617a29a8fc2588b1f93d81c9a1.png