带Projection的Spring JPA本机查询给出了"ConverterNotFoundException". [英] Spring JPA native query with Projection gives "ConverterNotFoundException"

问题描述

我正在使用Spring JPA，我需要一个本机查询.通过该查询，我只需要从表中获取两个字段，因此我尝试使用

I'm using Spring JPA and I need to have a native query. With that query, I need to get only two fields from the table, so I'm trying to use Projections. It isn't working, this is the error I'm getting:

org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [com.example.IdsOnly]

我试图严格遵循所链接页面的说明，试图使查询成为非本地查询(如果我使用投影，实际上我是否需要将查询设为本地查询，顺便说一句?)，但我总是会遇到该错误.
如果使用接口，则可以，但是结果是代理，因此我真的需要它们成为正常结果"，以便可以将其转换为json.

I tried to follow precisely the instructions of that page I linked, I tried to make my query non-native (do I actually need it to be native if I use projections, btw?), but I always get that error.
If I use an interface it works, but the results are proxies and I really need them to be "normal results" that I can turn into json.

所以，这是我的代码.实体:

So, here's my code. The Entity:

import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@NoArgsConstructor
@Entity
@Table(name = "TestTable")
public class TestTable {

    @Id
    @Basic(optional = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    @Column(name = "Id")
    private Integer id;
    @Column(name = "OtherId")
    private String otherId;
    @Column(name = "CreationDate")
    @Temporal(TemporalType.TIMESTAMP)
    private Date creationDate;
    @Column(name = "Type")
    private Integer type;
}

投影的类别:

import lombok.Value;

@Value // This annotation fills in the "hashCode" and "equals" methods, plus the all-arguments constructor
public class IdsOnly {

    private final Integer id;
    private final String otherId;
}

存储库:

public interface TestTableRepository extends JpaRepository<TestTable, Integer> {

    @Query(value = "select Id, OtherId from TestTable where CreationDate > ?1 and Type in (?2)", nativeQuery = true)
    public Collection<IdsOnly> findEntriesAfterDate(Date creationDate, List<Integer> types);
}

以及尝试获取数据的代码:

And the code that tries to get the data:

@Autowired
TestTableRepository ttRepo;
...
    Date theDate = ...
    List<Integer> theListOfTypes = ...
    ...
    Collection<IdsOnly> results = ttRepo.findEntriesAfterDate(theDate, theListOfTypes);  

感谢您的帮助.我真的不明白我在做什么错.

Thanks for the help. I really don't understand what I'm doing wrong.

推荐答案

使用spring数据，您可以剪切中间人并简单地定义

with spring data you can cut the middle-man and simply define

public interface IdsOnly {
  Integer getId();
  String getOtherId();
}

并使用本机查询，例如；

and use a native query like;

@Query(value = "Id, OtherId from TestTable where CreationDate > ?1 and Type in (?2)", nativeQuery = true)
    public Collection<IdsOnly> findEntriesAfterDate(Date creationDate, List<Integer> types);

签出 https://docs.spring .io/spring-data/jpa/docs/current/reference/html/#projections

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