JPA deleting bidirectional association from inverse side

Question

In my domain model there are a lot of bidirectional associations (both OneToMany and ManyToMany)

I've read this article and made all my associations on the basis of the sample pattern. (the ManyToMany associations has a two-sided addXY methods, following the pattern)

Using the pattern in this article the question is, what about deleting from the inverse side?

Example:

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); }
}

On the other side:

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);
}

The problem is, that the preRemove method causes ConcurrentException . How to handle this? The goal is, to delete the CustomerStatus, and set NULL all the Customers, where there was that status.

UPDATE

Without the preRemove method, I've got MySQLIntegrityConstraintViolationException: Cannot delete or update a parent row: a foreign key constraint fails

Answer 1

You cannot call this.customers.remove(c) while you are iterating over the customer collection. This question has come up before so you may find other solutions as in here: How to avoid ConcurrentModificationException when iterating over a map and changing values?

but a simple solution is to just create a new list from the old to iterate over on preRemove:

public void preRemove(){
    List<Customer> tempList = new ArrayList(customers);
    for(Customer c : tempList){
        c.setCustomerStatus(null); 
    }
}