Java 实体具有多对一关系时的DTO到实体映射

我试图将业务对象映射到实体中，但遇到了问题，不知道如何解决

问题是当我试图将这些属性从DTO映射到另一个表时，这些属性是多对一关系的属性

下面是我的

实体的样子：

@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;
... }

下面是
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
是具有与其在数据库中的主键相对应的分配编号的枚举。例如，
CarTypes
是：

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

这是我写的地图。如何根据
CarType
主键将适当的
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;
... }


根据CarType Id获取
CarType
实体。例如：

cartypecartype=entityManager.find（CarType.class，carTypeId）

然后将
CarEntity
中的
carType
设置为

carEntity.setCarType（carType）