QueryWrapper

组装查询条件

组装排序条件

组装删除条件

使用QueryWrapper实现修改功能

a>例1：组装查询条件

//查询用户名包含a，年龄在20到30之间，并且邮箱不为null的用户信息
    @Test
    public void test1(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.like("user_name","a")
                .between("age",20,30)
                .isNotNull("email");
        List list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

b>例2：组装排序条件

//按年龄降序查询用户，如果年龄相同则按id升序排列
    @Test
    public void test2(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.orderByDesc("age")
                .orderByAsc("uid");
        List list = userMapper.selectList(queryWrapper);
        list.forEach(System.out::println);
    }

c>例3：组装删除条件

//删除email为空的用户
    @Test
    public void test3(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        queryWrapper.isNull("email");
        int result = userMapper.delete(queryWrapper);
        System.out.println(result);
    }

d>例4：使用QueryWrapper实现修改功能

//将（年龄大于20并且用户名中包含有a）或邮箱为null的用户信息修改
    @Test
    public void test4(){
        QueryWrapper queryWrapper = new QueryWrapper<>();
        User user = new User();
        user.setName("小明");
        user.setEmail("xiaoming@qq.com");
        queryWrapper.gt("age",20)
                .like("user_name","a")
                .or()
                .isNull("email");
        int result = userMapper.update(user,queryWrapper);
        System.out.println(result);
    }