jpa - JPA: do i have to fetch all OneToMany relation list in order to add new relation

Question

lets say i have Entity A and A Has List of B which is mark as OneToMany. do i have to fetch all of B items in order to add new B item to the list A has?

example:

@Entity
public class A {

   @Id
   Long id;

   @OneToMany
   List<B> bs;
} 

do i have to fetch all of A.bs in order to add new item to bs ?

thanks

Alon

EDIT few more questions:

@German: interesting! few questions

1. what if the join between A and B is by Table C? do i get the same behavior?

2. why does the list make troubles?

3. what can i use instead of a list? Set?

4. if I persist A do i overwrite all the links for B?

5. what if the link is ManyToMany (using extra table)

Answer 1

您必须将 b 添加到 A 的 bs 列表中。但是会发生什么是特定于提供者的。启用更改跟踪后，EclipseLink 等一些提供程序可以避免为延迟加载列表上的某些操作获取列表

Answer 2

如果 B 有一个指向 A 的 @ManyToOne 注释并且您不会使用该列表，您可能只需要设置 B 对 A 的引用并将其持久化，而根本不需要触摸 A 实例。在数据库中，数据将被插入到表 B 中，但在内存中，A 的列表将没有新元素。