3.1、namespace

namespace 中必须指定Mapper 接口的全类名

3.2、select

3.2.1、编写接口

//根据id查询
    User getUserById(int id);

3.2.2、编写对应的mapper中的sql语句（mapper映射文件）

<select id="getUserById" parameterType="int" resultType="com.yan.bear.User">
        select * from mybatis.user where id = #{id}
    </select>
<!--
id:namespace中的方法名
parameterType:参数类型
resultType:sql语句执行的返回值
-->

3.2.3、测试

 @Test
    public void getUserId(){
        SqlSession sqlSession =  MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User userById = mapper.getUserById(1);
        System.out.println(userById);
        sqlSession.close();
    }

3.3、insert、delete、update

1. 编写接口//inset一个用户 int addUser(User user); //修改用户 int updateUser(User user); //删除用户 int deleteUser(int id);
2. 编写对应的mapper中的sql语句（mapper映射文件）<insert id="addUser" parameterType="com.yan.bear.User"> insert into mybatis.user (id, name, pwd) value (#{id},#{name},#{pwd}) </insert> <update id="updateUser" parameterType="com.yan.bear.User"> update mybatis.user set name = #{name},pwd = #{pwd} where id = #{id}; </update> <delete id="deleteUser" parameterType="com.yan.bear.User"> delete from mybatis.user where id = #{id} </delete>
3. 测试//增删改需要提交事务 @Test public void addUser(){ SqlSession sqlSession = MybatisUtils.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); int res = mapper.addUser(new User(4, "ly", "1111111")); if (res > 0){ System.out.println("插入成功！"); } sqlSession.commit(); //提交事务 sqlSession.close(); } @Test public void updateUser() { SqlSession sqlSession = MybatisUtils.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); int res = mapper.updateUser(new User(4,"hehhe","123123")); if (res > 0){ System.out.println("修改成功！"); } sqlSession.commit(); //提交事务 sqlSession.close(); } @Test public void deleteUser(){ SqlSession sqlSession = MybatisUtils.getSqlSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); int deleteUser = mapper.deleteUser(4); if (deleteUser > 0){ System.out.println("删除成功！"); } sqlSession.commit();//提交事务 sqlSession.close(); }

3.4、万能Map

如果实体类或者数据库中的表、字段或者参数很多，应当考虑Map

int addUser2(Map<String,Object> map);

<!--对象的属性，可以直接取出来
传递map的key
-->
<insert id="addUser" parameterType="map">
    insert into mybatis.user (id, name, pwd) value (#{userid},#{username},#{password})
</insert>

@Test
public void addUser2(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("userid",5);
    map.put("username","hh");
    map.put("password","123456");
    mapper.addUser2(map);
    sqlSession.close();
}

3.5、模糊查询

在Java执行代码中使用通配符% %

List<User> userList = mapper.getUserLike("%李%");

在sqlp拼接中使用通配符

<select id="getUserLike" resultType="com.yan.bear.User">
    select * from mybatis.user where name like "%"#{value}"%"
</select>

 //模糊查询
    List<User> getUserLike(String name);

<select id="getUserLike" resultType="com.yan.bear.User">
    select * from mybatis.user where name like ""#{value}
</select>

@Test
public void getUserLike(){
    SqlSession sqlSession =(SqlSession) MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    List<User> userList = mapper.getUserLike("%李%");
    for (User user : userList) {
        System.out.println(user);
    }
    sqlSession.close();
}