实体具有多对一关系时的 DTO 到实体映射

Question

我正在尝试将业务对象映射到实体，但卡住了，不知道如何解决。

问题是当我尝试从 DTO 映射这些属性时，这些属性是与另一个表的多对一关系的属性。

这是我的Entity 的样子：

@Entity
@Table(name = "t_car")
public class Car extends AbstractEntity implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue
@Column(name = "pkIdCar")
private Long id;

@Column(nullable = false, columnDefinition="VARCHAR(45)")
private String brand;

@Column(nullable = false)
private Integer productionYear;

@Column(nullable = false)
private Float engineCapacity;

@Column(nullable = false)
private Float power;

@Column(nullable = false)
private Integer distance;

@ManyToOne
@JoinColumn(name = "fkIdType")
private CarType carType;

@ManyToOne
@JoinColumn(name = "fkIdColor")
private Color color;
... }

这里是DTO：

public class CarDto {

private Long id;

private String brand;

private Integer productionYear;

private Float engineCapacity;

private Float power;

private Integer distance;

private CarTypes carType;

private ColorTypes color;
... }

CarTypes 和ColorTypes 是在数据库中分配了与其主键相对应的编号的枚举。例如CarTypes 是：

REGULAR_TWO_DOOR(1),
REGULAR_FOUR_DOOR(2),
STATION_WAGON(3),
MINIVAN(4),
SPORT(5),
LUXURY(6);

这是我设法编写的映射器。如何根据CarType 主键将正确的CarType（即实体）分配给carEntity？

public class CarMapper {

...
public static Car carDtoToCar(CarDto carDto, Car carEntity) {

    if(carEntity == null) {
        carEntity = new Car();
    }

    carEntity.setBrand(carDto.getBrand());
    carEntity.setProductionYear(carDto.getProductionYear());
    carEntity.setEngineCapacity(carDto.getEngineCapacity());
    carEntity.setPower(carDto.getPower());
    carEntity.setDistance(carDto.getDistance());

    Long carTypeId = Long.valueOf(carDto.getCarType().getNumber());
    Long carColorId = Long.valueOf(carDto.getColor().getNumber());

    /* ? */

    return carEntity;
}
}

CarType实体：

@Entity
@Table(name = "t_car_type")
public class CarType extends AbstractEntity implements Serializable {

private static final long serialVersionUID = 1L;

@Id
@GeneratedValue
@Column(name = "pkIdType")
private Long id;

@Enumerated(EnumType.STRING)
@Column(nullable = false, columnDefinition="VARCHAR(45)")
private CarTypes type;
... }

Answer 1

• 根据 Cartype Id 获取 CarType 实体。例如：
  CarType carType = entityManager.find(CarType.class, carTypeId);

• 然后将carType 中的CarEntity 设置为
  carEntity.setCarType(carType);