Spring JPA：JPQL查询返回空值

Question

我是 JPA 的新手...我从这个 JPQL 查询中得到一个空值。我正在尝试获取所有 ExamName 列数据，但它返回一个空值..

ExamRepository 接口：

    @Repository
    public interface ExamRepository extends JpaRepository<ExamEntity,Integer>
    {
        
      @Query("SELECT  e.ExamName from ExamEntity e")
      public List<ExamEntity> getExams();
    
    }
    

ExamEntity class: 
@Entity
@Table(name="exams")
public class ExamEntity {
     
     @Id
     @GeneratedValue
     @Column(length =100)
     private int id;
     
     @Column(nullable=false,length =100)
     private String ExamName;
     
     
     @Column(nullable=false,length =100)
     private String ExamDate;
    
    
}

Answer 1

您的选择和返回值有问题。如果您选择考试名称或选择实体，则需要返回一个字符串列表。

  @Query("SELECT  e.ExamName from ExamEntity e")
  public List<String> getExams();

或

  // This is redundant however as JpaRepository has findAll()
  @Query("SELECT  e from ExamEntity e")
  public List<ExamEntity> getExams();