条件构造器

我们写复杂SQL使用它来代替！

测试一

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

    @Test
    void contextLoads() {
        //查询name不为空、并且邮箱不为空、年龄大于等于20的
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.isNotNull("name").isNotNull("email").ge("age",20);
        userMapper.selectList(wrapper).forEach(System.out::println);//和刚才的map对比
    }
}

 测试二

 @Test
    void test2(){
        //查询名字 左小妹
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.eq("name","左小妹");
        User user = userMapper.selectOne(wrapper);
        System.out.println(user);
    }

测试三 

@Test
    void test3(){
        //查询年龄在20-30之间的用户
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.between("age",20,30);
        Long count = userMapper.selectCount(wrapper);
        System.out.println(count);
    }

 测试四

@Test
    void test4(){
        //模糊查询
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        //左和右 %e%
        wrapper.notLike("name","e").likeRight("email","t");
        List<Map<String, Object>> maps = userMapper.selectMaps(wrapper);
        maps.forEach(System.out::println);
    }

 测试五

  @Test
    void test5(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.inSql("id","select id from user where id<3");
        List<Object> objects = userMapper.selectObjs(wrapper);
        objects.forEach(System.out::println);
    }

测试六 

@Test
    void test6(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        //通过id降序排序
        wrapper.orderByDesc("id");
        List<User> users = userMapper.selectList(wrapper);
        users.forEach(System.out::println);
    }