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在Mybatis入门01–第一个Mybatis程序的基础上进行CRUD

1. namespace

namespace 中的包名要和 Dao/mapper 中的包名一致！

2. select、insert、update、delete

查询语句

• id：就是对应namespace中的方法名
• resultType：Sql语句执行的返回值
• parameterType：参数类型

步骤

1. 编写接口UserMapper.java

package com.ywm.mapper;import com.ywm.pojo.User;import java.util.List;//这里用mapper 等价于我以前用的Dao 以后都会用mapper
public interface UserMapper {// 获取全部用户List<User> getUserList();// 根据ID查询用户User getUserById(int id);// insert 一个用户int addUser(User user);// 修改一个用户int updateUser(User user);// 删除一个用户int deleteUser(int id);
}

2. 编写对应的 UserMapper.xml 中的Sql语句

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- namespace = 绑定一个对应的Mapper接口 -->
<!-- 千万不能写错!!!! -->
<mapper namespace="com.ywm.mapper.UserMapper"><!-- 查询语句 --><!-- 里面的id对应上面接口的方法名 --><select id="getUserList" resultType="com.ywm.pojo.User">select * from user</select><!--根据 id 查询用户，#{} 占位符取id--><select id="getUserById" parameterType="int" resultType="com.ywm.pojo.User">select * from user where id = #{id}</select><!--insert 一个用户, insert没有返回--><!--对象中的属性可以直接取出来--><insert id="addUser" parameterType="com.ywm.pojo.User">insert into mybatis.user (id, name, pwd) values (#{id}, #{name}, #{pwd});</insert><!--修改一个用户--><update id="updateUser" parameterType="com.ywm.pojo.User">update mybatis.user set name = #{name}, pwd = #{pwd}  where id = #{id};</update><!--删除一个用户--><delete id="deleteUser" parameterType="int">delete from mybatis.user where id = #{id};</delete></mapper>

3. 测试

需要特别注意的是：增删改需要提交事务

package mapper;import com.ywm.mapper.UserMapper;
import com.ywm.pojo.User;
import com.ywm.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;import java.util.List;public class UserMapperTest {@Testpublic void test() {// 第一步：获取sqlSession对象SqlSession sqlSession = MybatisUtils.getSqlSession();try {sqlSession = MybatisUtils.getSqlSession();// 执行SQL// 方法一：getMapper 建议使用UserMapper mapper = sqlSession.getMapper(UserMapper.class);List<User> userList = mapper.getUserList();// 方法二: 记住有这个方法就行// List<User> userList = sqlSession.selectList("mapper.UserMapper.getUserList");for (User user : userList) {System.out.println(user);}} catch (Exception e) {e.printStackTrace();} finally {// 关闭SqlSessionsqlSession.close();}}@Testpublic void getUserById(){// 第一步：获取sqlSession对象SqlSession sqlSession = MybatisUtils.getSqlSession();// 获取 mapperUserMapper mapper = sqlSession.getMapper(UserMapper.class);// 拿到对象User user = mapper.getUserById(1);// 输出System.out.println(user);// 关闭SqlSessionsqlSession.close();}// 增删改需要提交事务@Testpublic void addUser(){// 第一步：获取sqlSession对象SqlSession sqlSession = MybatisUtils.getSqlSession();// 获取 mapperUserMapper mapper = sqlSession.getMapper(UserMapper.class);// 拿到对象int res = mapper.addUser(new User(5,"哈哈","123123"));if (res > 0) {System.out.println("插入成功");}// 必须要写提交事务，才能插入成功sqlSession.commit();// 关闭SqlSessionsqlSession.close();}@Testpublic void uodateUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.updateUser(new User(4,"呵呵","123123123"));sqlSession.commit();sqlSession.close();}@Testpublic void deleteUser(){SqlSession sqlSession = MybatisUtils.getSqlSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);mapper.deleteUser(1);sqlSession.commit();sqlSession.close();}
}