JPA - 一个实体如何引用多对多关系中涉及的两个其他实体？

Question

我有以下表格：

在我的域模型中，我有一个Car 实体：

@Entity
@Data
public class Car {

    @Id
    private Long id;

    @ManyToMany
    @JoinTable(name="CarClassType",
        joinColumns= @JoinColumn(name="carId"),
        inverseJoinColumns = @JoinColumn(name="classTypeId"))
    private List<CarType> carTypes;
    
    private String model;
}

我还有一个 CarClassTypeSale 和 ClassType 实体。我没有CarClassType 实体。 CarClassTypeSale 类应该如何引用 Car 和 ClassType？

@Entity
@Data
public class CarClassTypeSale {

    @Id
    private Long id;

    @ManyToOne // this doesn't work; errors with invalid column name
    private Car car;

    @ManyToOne // this doesn't work; errors with invalid column name
    private ClassType classType;

}

Answer 1

此处的建模不需要@ManyToMany，因为您可以将CarClassType 建模为实体。由于CarClassType 表有一个附加列id，因此您实际上也不能以这种方式对其进行建模。如果你想要这个，你必须同时使用这两个 FK 作为主键并删除 id 列，我还是建议你这样做。

@Entity
@Data
public class Car {

    @Id
    private Long id;

    @OneToMany(mappedBy = "car")
    private Set<CarClassType> carTypes;
    
    private String model;
}
@Entity
@Data
public class CarClassType {

    @EmbeddedId
    private CarClassTypeId id;

    @ManyToOne(fetch = LAZY)
    @JoinColumn(name = "carId", insertable = false, updatable = false)
    private Car car;
    
    @ManyToOne(fetch = LAZY)
    @JoinColumn(name = "classTypeId", insertable = false, updatable = false)
    private CarType classType;

    @OneToMany(mappedBy = "carClassType")
    private Set<CarClassTypeSale> sales = new HashSet<>();
}
@Embeddable
@Data
public class CarClassTypeId {

    @Column(name = "carId")
    private Integer carId;
    
    @Column(name = "classTypeId")
    private Integer classTypeId;
}
@Entity
@Data
public class CarClassTypeSale {

    @Id
    private Long id;

    @ManyToOne
    private CarClassType carClassType;

    private LocalDate soldDate;


}

不确定CarClassTypeSale 是否适合这张图片。你的图表并没有真正告诉我这个类与其他类的关系。