学习笔记——Mybatis映射文件根标签与子标签

2023-01-09

一、Mybatis映射文件

1、映射文件根标签

mapping标签：

该标签中的namespace要求与接口的全类名一致

2、映射文件子标签

（1）cache（该命名空间的缓冲配置）

（2）cache-ref（引用其他命名空间的缓存配置）

（3）resultMap（描述如何从数据库结果集中加载对象，是最复杂也是最强大的元素）

注意：resultType解决不了的问题，交给resultMap（一般是多表查询）。

（4）sql（可被其他语句引用的可重用语句块）

（5）insert（映射插入语句）

（6）update（映射更新语句）

（7）delete（映射删除语句）

（8）select（映射查询语句）

3、示例代码

（1）“day02_mybatis.src.main.java.com.hh.mybatis.mapper.EmployeeMapper”中的代码

package com.hh.mybatis.mapper;
import com.hh.mybatis.pojo.Employee;
import java.util.List;
public interface EmployeeMapper {
    /**
     * 通过id获取员工信息
     * @param empId
     * @return
     */
    public Employee selectEmployee(int empId);
    /**
     * 添加员工信息
     * @param employee
     */
    public void insertEmployee(Employee employee);
    /**
     * 删除员工信息
     * @param empId
     */
    public void deleteEmployeeById(int empId);
    /**
     * 修改员工信息
     * @param employee
     */
    public void updateEmployee(Employee employee);
    /**
     * 查询所有员工信息
     * @return
     */
    public List<Employee> selectAllEmps();
}

（2）映射文件中的代码（day02_mybatis.src.main.resources.mapper下的EmployeeMapper.xml）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hh.mybatis.mapper.EmployeeMapper">
    <select id="selectEmployee" resultType="employee">
        SELECT
            id,
            last_name,
            email,
            salary
        FROM
            tbl_employee
        WHERE
            id=#{empId}
    </select>
    <insert id="insertEmployee">
        INSERT INTO
            tbl_employee(last_name,email,salary)
        VALUES
            (#{lastName},#{email},#{salary})
    </insert>
    <delete id="deleteEmployeeById">
        delete from
            tbl_employee
        where
            id=#{empId}
    </delete>
    <update id="updateEmployee">
        update
            tbl_employee
        set
            last_name = #{lastName},
            email = #{email},
            salary = #{salary}
        where
            id = #{id}
    </update>
    <select id="selectAllEmps" resultType="employee">
        SELECT
            id,
            last_name,
            email,
            salary
        FROM
            tbl_employee
    </select>
</mapper>

（3）测试类代码（day02_mybatis.src.test.java.TestMybatis）

import com.hh.mybatis.mapper.EmployeeMapper;
import com.hh.mybatis.pojo.Employee;
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.Test;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
public class TestMybatis {
    @Test
    public void TestMybatis(){
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            //通过sqlSessionFactory获取sqlSession对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            //获取EmployeeMapper的代理对象
            EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
            System.out.println("employeeMapper.getClass().getName() = " + employeeMapper.getClass().getName());
            Employee employee = employeeMapper.selectEmployee(1);
            System.out.println("employee = " + employee);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * 测试添加员工
     */
    @Test
    public void TestMybatisInsert(){
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            //通过sqlSessionFactory获取sqlSession对象
            SqlSession sqlSession = sqlSessionFactory.openSession();
            //获取EmployeeMapper的代理对象
            EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);
//            Employee wangwu = new Employee(null,"wangwu","zs@163.com",50.0);
            //测试添加员工信息
//            employeeMapper.insertEmployee(wangwu);
            //测试删除员工信息
//            employeeMapper.deleteEmployeeById(2);
//            Employee wangwu = new Employee(1,"zhangsan1","zs1@163.com",102.0);
//
//            employeeMapper.updateEmployee(wangwu);
            //查询所有员工信息
            List<Employee> employees = employeeMapper.selectAllEmps();
            for (Employee employee : employees) {
                System.out.println("employee = " + employee);
            }
            //提交事务
            sqlSession.commit();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}
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