[英]What is “the inverse side of the association” in a bidirectional JPA OneToMany/ManyToOne association?
[英]JPA deleting bidirectional association from inverse side
在我的領域模型中有很多雙向關聯(OneToMany 和 ManyToMany)
我已經閱讀了這篇文章並根據示例模式進行了所有關聯。 (ManyToMany 關聯具有雙面 addXY 方法,遵循模式)
使用本文中的模式,問題是,從反面刪除怎么樣?
例子:
public class Customer implements Serializable {
...
@ManyToOne()
private CustomerStatus customerStatus;
@PreRemove
public void preRemove(){
setCustomerStatus(null);
}
public void setCustomerStatus(CustomerStatus customerStatus) {
if(this.customerStatus != null) { this.customerStatus.internalRemoveCustomer(this); }
this.customerStatus = customerStatus;
if(customerStatus != null) { customerStatus.internalAddCustomer(this); }
}
另一方面:
public class CustomerStatus implements Serializable {
private static final long serialVersionUID = 1L;
@OneToMany(mappedBy="customerStatus")
private List<Customer> customers;
@PreRemove
public void preRemove(){
for(Customer c : customers){
c.setCustomerStatus(null); // this causes ConcurrentException
}
}
public List<Customer> getCustomers() {
return Collections.unmodifiableList(this.customers);
}
public void addCustomer(Customer c){
c.setCustomerStatus(this);
}
public void removeCustomer(Customer c){
c.setCustomerStatus(null);
}
void internalAddCustomer(Customer c){
this.customers.add(c);
}
void internalRemoveCustomer(Customer c){
this.customers.remove(c);
}
問題是, preRemove 方法導致ConcurrentException
。 如何處理? 目標是刪除 CustomerStatus,並將所有存在該狀態的客戶設置為 NULL。
更新
沒有 preRemove 方法,我有MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails
您不能在迭代客戶集合時調用 this.customers.remove(c)。 這個問題之前已經出現過,因此您可能會在這里找到其他解決方案: 如何在迭代地圖和更改值時避免 ConcurrentModificationException?
但一個簡單的解決方案是從舊列表中創建一個新列表以在 preRemove 上迭代:
public void preRemove(){
List<Customer> tempList = new ArrayList(customers);
for(Customer c : tempList){
c.setCustomerStatus(null);
}
}
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