1_sqlSession查询的三种方式

淩亂°似流年 2023-09-27 15:49 23阅读 0赞

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

![1e94a8eb3c8c6a5b4d13b7e4f36a76d0.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;
    }

![b04dd658ddcf4268d4f2505b34d19883.gif][]

![eb80ad43617df3cc647ca92a65e88497.gif][]

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>

![674ab5f3dcd959e5902aa7ab9394d184.gif][]

![a78d8b8a425cd5d547fcb756033ff86b.gif][]

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>

![ff7d1ca2dfc194a339ce96eb433890f8.gif][]

![6a5d08dda8eb20b34a47fd2c8a3690a2.gif][]

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();
        }
    }

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[1e94a8eb3c8c6a5b4d13b7e4f36a76d0.png]: https://img-blog.csdnimg.cn/img_convert/1e94a8eb3c8c6a5b4d13b7e4f36a76d0.png
[b04dd658ddcf4268d4f2505b34d19883.gif]: https://img-blog.csdnimg.cn/img_convert/b04dd658ddcf4268d4f2505b34d19883.gif
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[674ab5f3dcd959e5902aa7ab9394d184.gif]: https://img-blog.csdnimg.cn/img_convert/674ab5f3dcd959e5902aa7ab9394d184.gif
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