Question

我正在尝试使用弹簧数据jpa的@Query注释在mysql数据库上执行自定义查询。

表格是

+------------+---------------+------+-----+---------+-------+
| Field      | Type          | Null | Key | Default | Extra |
+------------+---------------+------+-----+---------+-------+
| id         | decimal(10,0) | NO   | PRI | NULL    |       |
| first_name | varchar(20)   | YES  |     | NULL    |       |
| last_name  | varchar(20)   | YES  |     | NULL    |       |
+------------+---------------+------+-----+---------+-------+

和mysql中的查询是

select last_name,count(last_name) as count from person group by last_name;

在Spring数据jpa中实现这一点。我使用这个逻辑，

创建另一个包含两个变量CountPerson和last_name

count

使用@Query编写查询，该方法返回CountPerson类对象列表。

弹簧数据jpa中的查询是

@Query("select p.lastName,count(p.lastName) as count from Person p group by p.lastName")

当代码编译并且Web服务器启动正常时，当我尝试运行相关方法时，我得到了

There was an unexpected error (type=Internal Server Error, status=500).
No aliases found in result tuple! Make sure your query defines aliases!; nested exception is java.lang.IllegalStateException: No aliases found in result tuple! Make sure your query defines aliases!

搜索此错误会显示spring data jpa: No aliases found in result tuple! Make sure your query defines aliases，表明这是一个固定的错误。所以我想我的问题是不同的

代码是

人类

//imports

@Entity
@Table(name = "person")
public class Person{

    @Id
    Long id;
    String firstName;
    String lastName;

    private Person(){}
    //constructor
}

人员存储库类

//imports
@Transactional
public interface PersonRepository extends CrudRepository<Person,Long>{

    @Query("select p.lastName,count(p.lastName) as count from Person p group by p.lastName")
    public List<CountPerson> countbylastname();
}

控制器类

@Controller
public class PersonController{

    @Autowired
    PersonRepository repository;

    @RequestMapping("/count")
    @ResponseBody
    public List<CountPerson> countbylastname(){
        return repository.countbylastname();
    }
}

计算人类

public class CountPerson{
    String lastName;
    int count;

    protected CountPerson(){}

    public CountPerson(String lastName,int count){
        this.lastName = lastName;
        this.count = count;
    }
}

Answer 1

更干净的解决方案是使用Spring Data JPA Projections：

Yo必须替换接口的类，并且只定义get方法：

public interface CountPerson {

    String getLastName();

    int getCount();
}

您的Repository方法如下所示：

@Query("select p.lastName as lastName,count(p.lastName) as count from Person p group by p.lastName")
public List<CountPerson> countbylastname();

Spring数据JPA：在结果元组中找不到别名！执行自定义查询时出错

1 个答案: