java - 我在 JPA 查询期间遇到转换类型错误，有效转换的最佳方法是什么？

Question

我收到以下错误:

"No converter found capable of converting from type [org.springframework.data.jpa.repository.query.AbstractJpaQuery$TupleConverter$TupleBackedMap] to type [de.hiqs.project.DTO.ProjectWithoutEmployeeDTO]"

导致错误的查询:

@Query("SELECT project.id, project.name, project.budget, " +
          "project.description, project.isArchived, project.archivedDate, " +
          "project.creationDate, project.customer.name AS customerName " +
          "FROM  Project project")
  List<ProjectWithoutEmployeeDTO> findAllWithoutEmployee();

我的实体:

@Data
@Entity
@ToString(exclude = {"employees"})
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Project {

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

  @Column(unique = true)
  private String name;

  private Integer budget;

  private String description;

  private Boolean isArchived;

  private LocalDate archivedDate;

  private LocalDate creationDate;

  @NotNull
  @ManyToOne
  private Customer customer;

  @OneToOne(cascade = CascadeType.ALL)
  private DefaultDailyEntrySettings defaultDailyEntrySettings;

  @ManyToMany
  @JoinTable(
          name = "employee_projects",
          joinColumns = @JoinColumn(name = "project_id"),
          inverseJoinColumns = @JoinColumn(name = "employee_id")
  )
  private List<Employee> employees;

DTO:

@Data
public class ProjectWithoutEmployeeDTO {

  private long id;
  private String name;
  private Integer budget;
  private String description;
  private Boolean isArchived;
  private LocalDate archivedDate;
  private LocalDate creationDate;
  private String customerName;
}

所以看来他无法将查询结果转换为ProjectWithoutEmployeeDTO。我认为它会自动计算出来，因为该类具有与查询结果完全相同的命名属性，但似乎并非如此。有效转换结果的最佳方法是什么？我可以返回一个对象列表而不是 ProjectWithoutEmployeeDTO 列表，并在服务内手动转换它，但这似乎不是最好的方法。

编辑:我设法做到了

@Query("SELECT new classpath.ProjectWithoutEmployeeDTO(project.id, project.name, project.budget, " +
          "project.description, project.isArchived, project.archivedDate, " +
          "project.creationDate, project.customer.name) " +
          "FROM  Project project")
  List<ProjectWithoutEmployeeDTO> findAllWithoutEmployee();

然后只需将该构造函数添加到 DTO 中，或者让 Lambok 使用 @AllArgsConstructor 自动执行此操作

Answer 1

您的查询应使用构造函数表达式:

@Query("SELECT NEW yourpackage.ProjectWithoutEmployeeDTO(project.id, project.name, project.budget, " +
       "project.description, project.isArchived, project.archivedDate, " +
       "project.creationDate, project.customer.name AS customerName) " +
       "FROM  Project project")

请注意，ProjectWithoutEmployeeDTO 必须是完全合格的