如何建立基于非关键字段的关系？

我模拟了你的用例，你可以在GitHub上找到测试。

这些是映射：

@Entity(name = "Car")
public static class Car implements Serializable {

    @Id
    @GeneratedValue
    long id;

    @Column(name="transmission", nullable = false)
    String transmission;
    @OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
    Set<CarFactory> factories;
}

@Entity(name = "Factory")
public static class Factory  implements Serializable {

    @Id
    @GeneratedValue
    long id;
}

@Entity(name = "CarFactory")
public static class CarFactory implements Serializable {

    @Id
    @ManyToOne
    @JoinColumn(name = "transmission", referencedColumnName = "transmission")
    Car car;

    @ManyToOne
    @Id
    Factory factory;

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

    public void setFactory(Factory factory) {
        this.factory = factory;
    }
}

以下是添加一些测试数据的方法：

doInTransaction(session -> {
    Car car = new Car();
    car.transmission = "Auto";

    Car car1 = new Car();
    car1.transmission = "Manual";

    Factory factory = new Factory();
    session.persist(factory);
    session.persist(car);
    session.persist(car1);

    CarFactory carFactory = new CarFactory();
    carFactory.setCar(car);
    carFactory.setFactory(factory);

    CarFactory carFactory1 = new CarFactory();
    carFactory1.setCar(car1);
    carFactory1.setFactory(factory);

    session.persist(carFactory);
    session.persist(carFactory1);
});

测试工作正常：

@Test
public void test() {
    doInTransaction(session -> {
        List<CarFactory> carFactoryList = session.createQuery("from CarFactory").list();
        assertEquals(2, carFactoryList.size());
    });
}

更新

由于以下唯一约束，您会收到异常：

alter table Car add constraint UK_iufgc8so6uw3pnyih5s6lawiv  unique (transmission)

这是正常行为，因为 FK 必须唯一标识 PK 行。就像不能有多个具有相同 PK 的行一样，不能让 FK 标识符引用多个行。

映射是问题所在。您需要引用其他内容，而不是 .您需要一个唯一的汽车标识符，如VIN（车辆识别码），因此您的映射将变为：transmision

@Entity(name = "Car")
public static class Car implements Serializable {

    @Id
    @GeneratedValue
    long id;

    @Column(name="vin", nullable = false)
    String vin;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "car")
    Set<CarFactory> factories;
}

@Entity(name = "CarFactory")
public static class CarFactory implements Serializable {

    @Id
    @ManyToOne
    @JoinColumn(name = "vin", referencedColumnName = "vin")
    Car car;

    @ManyToOne
    @Id
    Factory factory;

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

    public void setFactory(Factory factory) {
        this.factory = factory;
    }
}

这样，是唯一的，并且子关联可以引用一个且只能引用一个父项。vin

这里的问题是，您正在使用非主键字段作为外键，这似乎不正确，并且您的字段应该是唯一的，这行不正确：transmission

@JoinColumn(name="transmission",referencedColumnName = "transmission")

您在此处有一个映射，该映射需要在关联表中具有@EmbeddedId属性，并且您的代码应如下所示：Many-To-Many

汽车工厂类

@Entity
public class CarFactory {

   private CarFactoryId carFactoryId = new CarFactoryId();

   @EmbeddedId
   public CarFactoryId getCarFactoryId() {
       return carFactoryId;
   }

   public void setCarFactoryId(CarFactoryId carFactoryId) {
       this.carFactoryId = carFactoryId;
   }

   Car car;

   Factory factory;

   //getters and setters for car and factory
}

CarFactoryId 类

@Embeddable
public class CarFactoryId implements Serializable{

    private static final long serialVersionUID = -7261887879839337877L;
    private Car car;
    private Factory factory;

    @ManyToOne
    public Car getCar() {
        return car;
    }
    public void setCar(Car car) {
        this.car = car;
    }

    @ManyToOne
    public Factory getFactory() {
        return factory;
    }
    public void setFactory(Factory factory) {
        this.factory = factory;
    }
    public CarFactoryId(Car car, Factory factory) {
        this.car = car;
        this.factory = factory;
    }
    public CarFactoryId() {}

}

汽车类

@Entity
public class Car {

    @Id
    @GeneratedValue
    long id;
    @Column(name="transmission", nullable = false)
    String transmission;

    private Set<CarFactory> carFactories = new HashSet<CarFactory>();

    @OneToMany(mappedBy = "primaryKey.car",
    cascade = CascadeType.ALL)
    public Set<CarFactory> getCarFactories() {
        return carFactories;
    }

    ...

}

对于类也是如此，请注意有几种方法可以定义一个或一个，看看：Factoryembedded idcomposite id

• 使用复合主键和注释映射多对多。
• 如何使用批注创建休眠复合键

注意：

在我的示例中，我没有在复合ID中使用字段，但您可以使用它，您可以看到下面的示例：transmission

• 嵌入式主键