Spring引导接口投影仅返回null

Question

我使用的是spring数据jpa。目标是从我的条目表中仅获取列"；标题"；以及"；creation_date"；。显然，这是可能的东西，称为界面投影。所以我创建了接口，并将返回类型更改为接口，接口会被返回，但当我调用get方法/return it时，值只为null。

这是我的实体类：

import java.time.Instant;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import com.sun.istack.NotNull;
@Entity
public class Entry {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;

@Column(columnDefinition="timestamptz")
Instant creationDate;

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="userId")
@NotNull
private User user;

@Column(columnDefinition = "varchar(256)") 
String title;
@Column(columnDefinition = "text") 
String text;




public Entry() {
creationDate = Instant.now();
}


public long getId() {
return id;
}


public void setId(long id) {
this.id = id;
}


public Instant getCreationDate() {
return creationDate;
}


public void setCreationDate(Instant creationDate) {
this.creationDate = creationDate;
}


public User getUser() {
return user;
}


public void setUser(User user) {
this.user = user;
}


public String getTitle() {
return title;
}


public void setTitle(String title) {
this.title = title;
}


public String getText() {
return text;
}


public void setText(String text) {
this.text = text;
}




}

这是我的界面：

import java.time.Instant;

public interface EntryTitleDateAndUserIdDTO {
public String getTitle();
public Instant getCreationDate();
//User getUser();

}

这是我的存储库：

public interface EntryRepository extends JpaRepository<Entry, Long>{

@Query("SELECT e.title, e.creationDate FROM Entry e WHERE e.user = ?1")
ArrayList<EntryTitleDateAndUserIdDTO> getAllEntriesOfUser(User user);

@Query("SELECT e FROM Entry e WHERE e.id = ?1 AND e.user = ?2")
Entry getEntryOfUser(Long entryId, Long userId );

@Query("DELETE FROM Entry e WHERE e.id = ?1 AND e.user = ?2")
Entry deleteEntry(Long entryId, Long userId );
}

这是我的控制器：

@RestController
@RequestMapping("/User")
public class UserController {

@Autowired
UserRepository userRepo;

@Autowired
EntryRepository entryRepo;



@GetMapping("/{userId}/Entries")
private ArrayList<EntryTitleDateAndUserIdDTO> getAllEntries(@PathVariable Long userId) {

User u = userRepo.findById(userId).get();
ArrayList<EntryTitleDateAndUserIdDTO> e = entryRepo.getAllEntriesOfUser(u);



return e;

}

这是浏览器中的输出：

[{"title":null,"creationDate":null}]

这是数据库中的安全内容：Postgresql条目表

这是Spring生成的查询：

select
user0_.id as id1_1_0_,
user0_.email as email2_1_0_,
user0_.join_date as join_dat3_1_0_,
user0_.password as password4_1_0_,
user0_.username as username5_1_0_ 
from
public.user user0_ 
where
user0_.id=?
2021-11-04 18:13:35.417 TRACE 5104 --- [nio-8080-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [1]
2021-11-04 18:13:35.447 DEBUG 5104 --- [nio-8080-exec-1] org.hibernate.SQL                        : 
select
entry0_.title as col_0_0_,
entry0_.creation_date as col_1_0_ 
from
public.entry entry0_ 
where
entry0_.user_id=?
2021-11-04 18:13:35.448 TRACE 5104 --- [nio-8080-exec-1] o.h.type.descriptor.sql.BasicBinder      : binding parameter [1] as [BIGINT] - [1]

如果有人能帮忙，我们将不胜感激，提前表示感谢。

Answer 1

尝试对所选字段进行混叠，以完全匹配投影接口方法getTitle和getCreationDate

@Query("SELECT e.title as title, e.creationDate as creationDate FROM Entry e WHERE e.user = ?1")

Answer 2

由于您使用的是Spring Data JPA，因此可以使用派生查询，而不是注释所有查询。这也将消除对别名的需要。

public interface EntryRepository extends JpaRepository<Entry, Long>{

ArrayList<EntryTitleDateAndUserIdDTO> findByUser(User user);

Entry findByIdAndUserId(Long id, Long userId );

void deleteByIdAndUserId(Long id, Long userId );
}