java - 为什么在持久化 JoinTable 对象时我的 OneToMany 列表没有填充？

Question

我正在开发一个 hibernate 项目，并且 Car 和 CarDriver 之间有一个 @ManyToMany 关系。问题是这种关系也有属性，因此我使用一个连接到 Car 和 CarDriver 的单独实体，这个实体称为 CarUsage。

我的问题是，当我保留 CarUsage 对象时，Car 和 CarDriver 中的 CarUsage 列表不会填充这个新对象。

这是我的实体:

汽车:

@Entity
@Table(name = "car")
@Inheritance(strategy = InheritanceType.JOINED)
public class Car extends BaseEntity {

@Column(name = "registration_plate")
private String registrationPlate;

@OneToMany(mappedBy="car")
private List<CarUsage> carUsages;

public String getRegistrationPlate() {
    return registrationPlate;
}

public void setRegistrationPlate(String registrationPlate) {
    this.registrationPlate = registrationPlate;
}

public List<CarUsage> getCarUsages() {
    return carUsages;
}

public void setCarUsages(List<CarUsage> carUsages) {
    this.carUsages = carUsages;
}
}

汽车司机

@Entity
@Table(name="car_driver")
public class CarDriver extends BaseEntity {

@OneToMany(mappedBy="carDriver")
private List<CarUsage> carUsages;

public List<CarUsage> getCarUsages() {
    return carUsages;
}

public void setCarUsages(List<CarUsage> carUsages) {
    this.carUsages = carUsages;
}
}

还有我的 JoinTable CarUsage:

@Entity
@Table(name = "car_usage")
public class CarUsage extends BaseEntity {

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "car_id")
private Car car;
@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "car_driver_id")
private CarDriver carDriver;
@Column(name = "start_date")
private Date startDate;
@Column(name = "end_date")
private Date endDate;
@Column(name = "active", nullable = false)
private boolean active;

public Car getCar() {
    return car;
}

public void setCar(Car car) {
    this.car = car;
}

public CarDriver getCarDriver() {
    return carDriver;
}

public void setCarDriver(CarDriver carDriver) {
    this.carDriver = carDriver;
}

public Date getStartDate() {
    return startDate;
}

public void setStartDate(Date startDate) {
    this.startDate = startDate;
}

public Date getEndDate() {
    return endDate;
}

public void setEndDate(Date endDate) {
    this.endDate = endDate;
}

public boolean isActive() {
    return active;
}

public void setActive(boolean active) {
    this.active = active;
}
}

当我保留新的 CarUsage 时，Car 和 CarDriver 中的列表不会更新。

CarUsage carUsage = carUsageCreator.makeCarUsage(companyCar, carDriver, new Date(), new Date(), true);
    carUsageDao.persist(carUsage);

有人知道我做错了什么吗？

Answer 1

尝试使用 JPA/Hibernate 级联:

选择关系的所有者方

汽车 > CarUsage > CarDriver 或 CarDriver > CarUsage > Car。

如果CarDriver是车主端，则映射应该是

@OneToMany(mappedBy="carDriver",cascade = CascadeType.ALL, orphanRemoval = true)
private List<CarUsage> carUsages;

要创建新的 carUsage 关系，您可以创建如下方法:

public void driveCar(CarDriver carDriver, Car car){
    CarUsage carUsage = new CarUsage(carDriver, car, Date()....)
    carDriver.getCarUsages().add(carUsage);
    car.getCarUsages().add(carUsage);// Just to maintain coherence for the rest of the current transaction
      ...
}

如果您处于事务中，此代码将自动保留 carUsage 实例。 (不再需要 carUsageDao.persist(carUsage))..