问题描述
我想我误解了在@ManyToOne关系中级联的含义.
情况:
public class User {
@OneToMany(fetch = FetchType.EAGER)
protected Set<Address> userAddresses;
}
public class Address {
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
protected User addressOwner;
}
cascade = CascadeType.ALL的含义是什么?例如，如果我从数据库中删除某个地址，那么添加cascade = CascadeType.ALL的事实如何影响我的数据(我猜是User)?
CascadeType.ALL的含义是，持久性会将所有EntityManager操作(PERSIST, REMOVE, REFRESH, MERGE, DETACH)传播(层叠)到相关实体.在您看来，这是个坏主意，因为删除Address会导致删除相关的User.由于用户可以有多个地址，因此其他地址将成为孤立地址.但是，相反的情况(用User注释)是有道理的-如果一个地址仅属于一个用户，则删除该用户可以安全地传播对属于该用户的所有地址的删除.
顺便说一句:您可能想在User中添加mappedBy="addressOwner"属性，以向持久性提供程序发出信号，告知联接列应位于ADDRESS表中.
I think I misunderstood the meaning of cascading in the context of a @ManyToOne relationship.
The case:
public class User {
@OneToMany(fetch = FetchType.EAGER)
protected Set<Address> userAddresses;
}
public class Address {
@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
protected User addressOwner;
}
What is the meaning of the cascade = CascadeType.ALL? For example, if I delete a certain address from the database, how does the fact that I added the cascade = CascadeType.ALL affect my data (the User, I guess)?
The meaning of CascadeType.ALL is that the persistence will propagate (cascade) all EntityManager operations (PERSIST, REMOVE, REFRESH, MERGE, DETACH) to the relating entities.
It seems in your case to be a bad idea, as removing an Address would lead to removing the related User. As a user can have multiple addresses, the other addresses would become orphans. However the inverse case (annotating the User) would make sense - if an address belongs to a single user only, it is safe to propagate the removal of all addresses belonging to a user if this user is deleted.
BTW: you may want to add a mappedBy="addressOwner" attribute to your User to signal to the persistence provider that the join column should be in the ADDRESS table.
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