@SpringBootTest
public class WrapperTest {
    @Autowired
    private UserMapper userMapper;

    @Test
    void contextLoads() {

        QueryWrapper<User> wrapper = new QueryWrapper<>();
        //查询name和email不为空，年龄大于等于12。
        wrapper
                .isNotNull("name")
                .isNotNull("email")
                .ge("age", 12);
        userMapper.selectList(wrapper).forEach(System.out::println);
    }

    @Test
    void test1() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        //查询年龄在20到30之间
        wrapper.between("age", 20, 30);
        Integer count = userMapper.selectCount(wrapper);
        System.out.println(count);
    }

    @Test
    void test2() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        //查询名字=XXX
        wrapper.eq("name", "兰姐姐");
        userMapper.selectList(wrapper).forEach(System.out::println);

    }
}

模糊查询

    //模糊查询
    @Test
    void tet4() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper
                .notLike("name", "e")  // %e%
                .likeRight("email", "t");    // % 在左和右   t%
        List<Map<String, Object>> maps = userMapper.selectMaps(wrapper);
        maps.forEach(System.out::println);

    }
}

 void test5() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();

        //id 在字查询中查出来
        wrapper.inSql("id", "select id from user where id>2");
        List<Object> objects = userMapper.selectObjs(wrapper);
        objects.forEach(System.out::println);
    }

 @Test
    void test6() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        // 通过 id 进行排序
        wrapper.orderByDesc("id");
        List<Object> objects = userMapper.selectObjs(wrapper);
        objects.forEach(System.out::println);
    }