Spring Boot. how to Pass Optional<> to an Entity Class

Question

i am currently making a website using spring and i stumble upon this basic scenario that i don't have any idea on how to solve this specific code: Entity = Optional;

RoomEntity roomEntity =  roomRepository.findById(roomId);

ReservationResource(API request Class):

    public class ReservationResource {
    @Autowired
    RoomRepository roomRepository;

    @RequestMapping(path = "/{roomId}", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
    public ResponseEntity<RoomEntity> getRoomById(
    @PathVariable
    Long roomId){
        RoomEntity roomEntity =  roomRepository.findById(roomId);
        return new ResponseEntity<>(roomEntity, HttpStatus.OK);}
    }}

RoomRepository Class:

public interface RoomRepository extends CrudRepository<RoomEntity, Long> {
    List<RoomEntity> findAllById(Long id);
}

RoomEntity

@Entity
@Table(name = "Room")
public class RoomEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @NotNull
    private Integer roomNumber;

    @NotNull
    private String price;

    public RoomEntity() {
        super();
    }
}

Answer 1

According to your error you are getting Optional<RoomEntity> from repository's findAll method and you are casting it to RoomEntity .

Instead of RoomEntity roomEntity = roomRepository.findById(roomId); do this

Optional<RoomEntity> optinalEntity = roomRepository.findById(roomId); RoomEntity roomEntity = optionalEntity.get();

Answer 2

The answers lack some job to do. Before you call get() , you should do some checking with isPresent() . Like so:

Optional<RoomEntity> optionalEntity =  roomRepository.findById(roomId);
if (optionalEntity.isPresent()) {
    RoomEntity roomEntity = optionalEntity.get();
    ...
}

Read this great article about optionals: https://dzone.com/articles/using-optional-correctly-is-not-optional

Answer 3

试试这个，它对我有用

RoomEntity roomEntity = roomRepository.findById(roomId).orElse(null);

Answer 4

First solution

You can implement JpaRepository instead of CrudRepository which provide a getOne method that returns an RoomEntity as you expect. ( JpaRepository for JPA or MongoRepository for MongoDB) :

public interface RoomRepository extends JpaRepository<RoomEntity, Long> {
    List<RoomEntity> findAllById(Long id);
}

and

RoomEntity roomEntity = roomRepository.getOne(roomId);

Note that an EntityNotFoundException will be thrown if there's no RoomEntity for this roomId.

Second solution

The findById method of CrudRepository returns an optional so you must deal with it properly to get an RoomEntity if there is one. For example :

RoomEntity roomEntity = optionalEntity.roomRepository.findById(roomId).get();

In this case .get() will throw a NoSuchElementException if there's no RoomEntity for this roomId.

This article may help to understand optionals : http://www.baeldung.com/java-optional

Answer 5

进行此铸造的最短方法

RoomEntity roomEntity = roomRepository.findById(roomId).get();

Answer 6

As @kaush-athukorala said, you need just add .get() at the end of RoomEntity roomEntity = roomRepository.findById(roomId); It works

You'll have RoomEntity roomEntity = roomRepository.findById(roomId).get();

Answer 7

RoomEntity roomEntity = roomRepository.findById(id).get();

这将解决您的错误！