@ManyToOne JPA关联的CascadeType.ALL是什么意思 [英] What is the meaning of the CascadeType.ALL for a @ManyToOne JPA association

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)?

解决方案

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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