Java JPA如何将一个实体实例与另一个实体的所有实例关联起来？

Question

我使用嵌入式 H2 数据库，其中使用 @OneToMany 关系将实体实例(产品)与其他实体(供应商)的多个实例相关联；当我有特定产品的特定供应商时，它很有用。但现在，我想将所有供应商与每一个产品关联起来；我不想在我的供应商表中为每个产品生成不同的供应商记录，而是我只想在我的供应商表中只有 5 条记录(5 个供应商)，这些记录与每个产品相关联，这几句话我想实现一些目标像“one to all”一样，是否可以使用JPA注释来做到这一点？

产品实体

@Entity
public class Product {

    @Id
    private String productCode;

    @OneToMany
    @JoinColumn(name = "supplier_id", referencedColumnName = "productCode")
    private List<Supplier> suppliers;

}

供应商实体

@Entity
public class Supplier {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "id")
    private Long id;

    private String name;
}

Answer 1

单向@OneToMany关联:

@Entity
public class Product {

    @Id
    // @Column(name = "id") maybe
    // @GeneratedValue maybe
    private String productCode;

    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true) // according to your need
    private List<Supplier> suppliers;

    ...
}

而且，

@Entity
public class Supplier {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    private String name;

    ...
}

@ManyToOne 关联:

@Entity
public class Product {

    @Id
    // @Column(name = "id") maybe
    // @GeneratedValue maybe
    private String productCode;

    ...
}

而且，

@Entity
public class Supplier {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    @ManyToOne
    @JoinColumn(name = "product_id", foreignKey = @ForeignKey(name = "PRODUCT_ID_FK"))
    private Product product;

    private String name;

    ...
}