我無法保存實體（Spring Boot 應用程序）

Question

@Entity(name = "cities")
public class City {

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

@Column(length = 256, unique = true, nullable = false)
private String name;

@Column(length = 4, nullable = false, unique = true)
private String code;

//    @OneToMany(mappedBy="city")
@OneToMany(cascade = CascadeType.ALL , orphanRemoval = true)
@JoinColumn(name = "city_id")
private List<ParkingFacility> parkingFacilities = new ArrayList<>();

@OneToMany(mappedBy="city")
private List<Vehicle> vehicles = new ArrayList<>();

---

@Entity(name = "parking_facilities")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class ParkingFacility {

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
protected Integer id;

@Column(length = 256, unique = true, nullable = false)
protected String name;


protected Integer capacity = 0;

@Column(name = "available_capacity")
protected  Integer availableCapacity = 0;

//    @ManyToOne(cascade=CascadeType.ALL)
//    @JoinColumn(name="city_id", nullable=false)
@ManyToOne(fetch = FetchType.EAGER)
protected City city;

@OneToMany(mappedBy="parkingFacility")
private List<Vehicle> vehicles;

---

public class ParkingFacilityDto {

protected Integer id;
@NotBlank @Length(max = 256)
protected String name;
@Min(0)
protected Integer capacity;
@Min(0)
protected Integer availableCapacity;
@NotBlank @Length(max = 256)
protected String city;

---

public class ParkingFacilityMapper {



public static ParkingFacility toFacility(ParkingFacilityDto facilityDto) {

    return ParkingFacility.builder()
            .name(facilityDto.getName())
            .capacity(facilityDto.getCapacity())
            .availableCapacity(facilityDto.getAvailableCapacity())
            .city(new City(InputFormatter.formatCityName(facilityDto.getCity())))
            .build();

}

}

我正在嘗試為給定城市保存停車設施，但出現此錯誤：

org.hibernate.TransientPropertyValueException: object references an unsaved transient 
instance - save the transient instance before flushing : 
com.goosfraba.city_parking.parking_facilities.model.ParkingFacility.city -> 
com.goosfraba.city_parking.cities.model.City; nested exception is 
java.lang.IllegalStateException: org.hibernate.TransientPropertyValueException: object 
references an unsaved transient instance - save the transient instance before flushing : 
com.goosfraba.city_parking.parking_facilities.model.ParkingFacility.city -> com.goosfraba.city_parking.cities.model.City",

我看到很多人建議在 StackOverflow 上提出的類似問題上使用 CascadeType.All，但如您所見，我已經在使用它，但仍然出現此錯誤。

請幫助我，因為我不知道從這里要做什么

Answer 1

將cascade = CascadeType.ALL添加到：

@ManyToOne(fetch = FetchType.EAGER)
protected City city

這將解決您的問題。