我是否必须为连接的查询创建单独的 @Entity 类才能提取结果？ 存储库

Question

I would like to pull data from two @Entity tables using Spring Boot JPA Repository (and display it in .html thymeleaf).

Challenge: I don't really want to have a separate @Entity class (thus a separate table) to represent the joined result. Is it even possible? I'm new to Spring and unsure what's the best practice.

Class Client

@Data
@Entity
@Table(name="client", uniqueConstraints={@UniqueConstraint(columnNames={"client_id"})})
public class Client {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "client_seq")
    @SequenceGenerator(name = "client_seq", initialValue = 50)
    @Column(name="client_id", nullable = false, unique = true, length = 9)
    private long client_id;
    @Column(name="NAME", nullable = false,  length = 20)
    private String name;
    @Column(name="SURNAME", nullable = false,  length = 20)
    private String surname;
    @Column(name="CITY", nullable = false,  length = 20)
    private String city;
    @Column(name="COUNTRY", nullable = false,  length = 20)
    private String country;
    @Column(name="BIO", nullable = false,  length = 200)
    private String bio;

    @OneToMany(mappedBy = "client")
    private Set<Request> requests;

    public Client() {
    }

    public Client(String name, String surname, String city, String country, String bio) {
        this.name = name;
        this.surname = surname;
        this.city = city;
        this.country = country;
        this.bio = bio;
    }

Class Request

@Entity
@Data
@Table(name="request",uniqueConstraints = {@UniqueConstraint(columnNames = "request_id")})
public class Request {

    public enum Status
    {
        PENDING, BACKED, DONE;
    }

    @Id
    @Column(name = "request_id", unique = true, nullable = false, length = 9)
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private long requestId;

    @ManyToOne
    @JoinColumn(name="client", referencedColumnName = "client_id")
    private Client client;

    @Column(name="request_short", nullable = false,  length = 100)
    private String requestShort;

    @Column(name = "request_long", nullable = false,  length = 250)
    private String requestLong;

    @Column(name = "request_date", nullable = false)
    private LocalDate requestDate;

    @Column(name = "status")
    private Status status;

    public Request(String requestShort, String requestLong, LocalDate requestDate, Status status) {
        this.requestShort = requestShort;
        this.requestLong = requestLong;
        this.requestDate = requestDate;
        this.status = status;
    }

}

DEMO class to collect the result but do not store it

@Data
@Component
public class ClientRequest {

    private long client_id;
    private long requestId;

    public ClientRequest(){};

    public ClientRequest(long client_id, long requestId) {
        this.client_id = client_id;
        this.requestId = requestId;
}

Finally my repository:

@Repository
public interface ClientRepository extends JpaRepository<Client, Long> {

    List<Client> findByName(String name);    // **works**

    @Query("SELECT a FROM Client a WHERE client_id > ?1")
    List<Client> findByUser_id(Long user_id);             // **works**

    @Query("SELECT a.client_id, b.request_id FROM Client a JOIN a.Request b WHERE a.client_id > ?1")
    List<ClientRequest> findPendingRequestsWithUserData(Long user_id);     // fails

  }

Relevant error MSG:

Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'webController': Unsatisfied dependency expressed through field 'clientRepository'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'clientRepository': Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Validation failed for query for method public abstract java.util.List com.dev.repository.ClientRepository.findPendingRequestsWithUserData(java.lang.Long)!

Answer 1

Try this. This should work.

@Query("SELECT new com.path.to.ClientRequest(a.client_id, b.request_id) FROM Client a JOIN a.requests b WHERE a.client_id > ?1")
List<ClientRequest> findPendingRequestsWithUserData(Long user_id); 

You need to create new object using new and full path of the class. That is what is missing.