JPA：如何刪除單向多對多關係中的鏈接記錄？

Question

我有一個單向多對多的實體'活動'和'發票'映射。該映射僅在Activity實體中設置（我不需要從Invoice端訪問活動）。

@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，但我有刪除活動的問題。該刪除的活動代碼如下：

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

當我運行這些代碼，我認爲EM將刪除第一個連接表中的記錄，然後刪除活動記錄（發票記錄應保持不變）。但連接表中的記錄永遠不會被刪除。我得到這個外鍵錯誤：

[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`....... 

我在做什麼錯在這裏？請幫助，謝謝。

Answer 1

我認爲你需要@ManyToMany(cascade = {CascadeType.REMOVE})選項。

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

在活動時間：

@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; 

顯然REMOVE不應與@ManyToMany使用（從JPA 2.0規範。）：

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.

你可以試試供應商擴展@OnDelete在休眠：

@OnDelete(action=OnDeleteAction.CASCADE)

或者你也可以手動做到這一點：

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

也可以將標註@PreRemove： 添加以下方法不是關係（發票）的所有者

實體

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