CRUD

CRUD

• 3.1、namespace

  • namespace中的包名要和Dao/mapper接口的包名一致

  3.2、select(查询)

  选择，查询语句

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

3.2.1、编写接口

//根据ID查询用户
User getUserByID(int id);

3.2.2、编写对应的mapper中的sql语句

<select id="getUserByID" parameterType="int" resultType="com.saxon.pojo.User">
        select * from users where id = #{id}
</select>

3.2.3、测试

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

3.3、insert(插入)

3.3.1、编写接口

//insert一个用户
int addUser(User user);

3.3.2、编写对应的mapper中的sql语句

<insert id="addUser" parameterType="com.saxon.pojo.User">
        insert into users (id, name, pwd) VALUES (#{id}, #{name}, #{pwd})
</insert>

3.3.3、测试

@Test
public void testAddUser(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int num = mapper.addUser(new User(4, "王五", "3132121"));
    if (num > 0){
        System.out.println("插入成功");
    }
    //增删改一定要提交事务
    sqlSession.commit();
    sqlSession.close();
}

3.4、update(修改)

3.4.1、编写接口

//update一个用户
int updateUser(User user);

3.2.2、编写对应的mapper中的sql语句

<update id="updateUser" parameterType="com.saxon.pojo.User">
    update users set name = #{name}, pwd=#{pwd} where id = #{id};
</update>

3.2.3、测试

@Test
public void testUpdate(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    mapper.updateUser(new User(1, "六六六", "3423243"));
    sqlSession.commit();
    sqlSession.close();
}

3.5、delete(删除)

3.5.1、编写接口

//删除一个用户
int deleteUser(int id);

3.5.2、编写对应的mapper中的sql语句

<delete id="deleteUser" parameterType="int">
    delete from users where id=#{id}
</delete>

3.5.3、测试

@Test
public void testDelete(){
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int i = mapper.deleteUser(4);
    if (i > 0){
        System.out.println("删除成功");
    }
    sqlSession.commit();
    sqlSession.close();
}

3.6、注意点

• 增删改需要提交事务