JPA：如何删除单向多对多关系中的链接记录？

Question

我有一个单向多对多的实体'活动'和'发票'映射。该映射仅在Activity实体中设置（我不需要从Invoice端访问活动）。

@ManyToMany 
@JoinTable(name = "OP_ACTIVITY_INVOICE_XREF", joinColumns = @JoinColumn(name = "ACTIVITY_ID", referencedColumnName = "OBJECT_ID"), inverseJoinColumns = @JoinColumn(name = "INVOICE_ID", referencedColumnName = "OBJECT_ID")) 
private Set<Invoice> invoices; 

插入和更新工作正常，但我有删除活动的问题。该删除的活动代码如下：

activity.getInvoices().clear(); 
    em.remove(activity); 

当我运行这些代码，我认为EM将删除第一个连接表中的记录，然后删除活动记录（发票记录应保持不变）。但连接表中的记录永远不会被删除。我得到这个外键错误：

[STDOUT] Hibernate: delete from OP_ACTIVITY where OBJECT_ID=? 
[JDBCExceptionReporter] SQL Error: 1451, SQLState: 23000 
ERROR [JDBCExceptionReporter] Cannot delete or update a parent row: a foreign key constraint fails (`prod/op_activity_invoice_xref`....... 

我在做什么错在这里？请帮助，谢谢。

Answer 1

我认为你需要@ManyToMany(cascade = {CascadeType.REMOVE})选项。

CascadeType.REMOVE: When deleting an entity, also delete the entities held in this field.

在活动时间：

@ManyToMany(cascade = {CascadeType.REMOVE}) 
@JoinTable(name = "OP_ACTIVITY_INVOICE_XREF", joinColumns = @JoinColumn(name = "ACTIVITY_ID", referencedColumnName = "OBJECT_ID"), inverseJoinColumns = @JoinColumn(name = "INVOICE_ID", referencedColumnName = "OBJECT_ID")) 
private Set<Invoice> invoices; 

显然REMOVE不应与@ManyToMany使用（从JPA 2.0规范。）：

The relationship modeling annotation constrains the use of the cascade=REMOVE specification. The cascade=REMOVE specification should only be applied to associations that are specified as OneToOne or OneToMany. Applications that apply cascade=REMOVE to other associations are not portable.

你可以试试供应商扩展@OnDelete在休眠：

@OnDelete(action=OnDeleteAction.CASCADE)

或者你也可以手动做到这一点：

for (Invoice invoice : activity.getInvoices()) { 
    em.remove(invoice); 
} 
activity.getInvoices().clear(); 
em.remove(activity); 
... flush() etc... 

也可以将标注@PreRemove： 添加以下方法不是关系（发票）的所有者

实体

@PreRemove 
private void removeInvoicesFromActivities() { 
    for (Activity a : activities) { 
     a.getInvoices().remove(this); 
    } 
}