java 使用 Hibernate 删除父行时如何删除所有子行？
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How to delete all child rows when parent is deleted using Hibernate?
提问by Eugene Mironenko
I have 2 tables.
我有2张桌子。
// Accounts
@OneToMany(mappedBy="accounts", cascade=CascadeType.ALL)
@Cascade(org.hibernate.annotations.CascadeType.ALL)
private Set<Mails> mails;
// Mails
@ManyToOne(cascade=CascadeType.ALL)
@JoinColumn(name="user_id" , referencedColumnName="id", insertable=false, updatable=false)
private Accounts accounts;
How can I organize deleting all child rows when the parent row will be deleted? I have tried to set CascadeType.DELETE_ORPHANfor the Accountstable, but with that I can't delete parent rows if a child row exists.
当父行将被删除时，如何组织删除所有子行？我试图CascadeType.DELETE_ORPHAN为Accounts表设置，但是如果存在子行，我无法删除父行。
回答by marekful
The problem probably is that the relation is defined in the wrong direction. Presuming that you have an accounttable with one-to-many relation to a mailtable, you will end up not being able to delete a record from accountuntil it has associated mailrows if you define the relation on accountto reference mail. The correct way is to create the foreign key on mailto reference account.
问题可能是关系的定义方向错误。假设您有一个account与表具有一对多关系的mail表，如果您将关系定义为引用，您将最终无法从中删除记录，account直到它具有关联的mail行。正确的方法是在引用上创建外键。accountmailmailaccount
With ON DELETE CASCADE, you tell MySQL that it should delete a row (whose table has the foreign key) ifits parent (referenced by the key) is deleted. This operation is allowed by definition because in such a case the deleted record has references to it. In contrast, a deletion is not allowed if a record has references pointing to other records from it.
使用ON DELETE CASCADE，你告诉 MySQL如果它的父行（由键引用）被删除，它应该删除一行（其表有外键）。根据定义，此操作是允许的，因为在这种情况下，已删除的记录具有对它的引用。相反，如果一个记录有指向其他记录的引用删除不允许从它。
回答by srikanth yaradla
You are using cascade=CascadeType.ALL in both entities. Try using that only at parent. This should work
您在两个实体中都使用了 cascade=CascadeType.ALL。尝试仅在父级使用它。这应该工作
//Accounts
@OneToMany(mappedBy="accounts", cascade=CascadeType.ALL,orphanRemoval=true)
private Set<Mails> mails;
//Mails
@ManyToOne
@JoinColumn(name="user_id" , referencedColumnName="id" , nullable=false)
private Accounts accounts;
回答by samlewis
The "mappedBy" property indicates that the other side owns the relationship, so in your case Mails owns the relationship which is probably not what you want.
“mappedBy”属性表示另一方拥有该关系，因此在您的情况下，Mails 拥有可能不是您想要的关系。
JPA Cascades only work in one direction, from the owner of the relationship.
JPA Cascades 只在一个方向上工作，来自关系的所有者。
So if you want Mails to be deleted when deleting an Account, you need to switch the owner of the relationship:
所以如果你想在删除一个Account时删除Mails，你需要切换关系的所有者：
//Accounts
@OneToMany(cascade=CascadeType.ALL)
private Set<Mails> mails;
//Mails
@ManyToOne(mappedBy="mails")
@JoinColumn(name="user_id" , referencedColumnName="id", insertable=false, updatable=false)
private Accounts accounts;
