使用Nhibernate删除对象时遇到问题

Question

I have some problems with deleting object. I am getting the following error:

[Test.Item#ab9a9869-b2c1-4262-8d33-9dd9010abd96][SQL: DELETE FROM InvoerItem WHERE DbId = ? AND Version = ?]

The DELETE statement conflicted with the REFERENCE constraint "FK9100B9F130A0A610". The conflict occurred in database "", table "dbo.InvoerItemToInvoerItem", column 'Listener_id'.

The situation is like this i have an object that has a collection of references to other objects of the same kind these are called listerners.

The mapping for the object looks like this :

public InvoerItemMap()
{
    HasManyToMany(x => x.Listeners)
        .ChildKeyColumn("Listener_id")
        .Cascade.None()
        .Access.CamelCaseField(Prefix.Underscore);
}

What is it that causes the exception when deleting an object that has a listeners connected to it? Do I have to inverse the relation ship of the listeners?

Answer 1

No, inverse doesn't help.

you need to specify what you want to do with the listeners. There are basically two options:

• tell the user that there are listeners around and he can't delete this object
• unregister the listeners by the software.

If you decide to unregister the listeners, then ... just implement it.

InvoerItem itemToDelete = ...;
itemToDelete.Listeners.Clear();
session.Delete(itemToDelete);

It would be even better to let the entity manage the listeners:

itemToDelete.UnregisterListeners();

Edit : if you have references from the listeners to the invoerItems, you need to remove them as well:

public void UnregisterListeners()
{
    foreach(Listener listener in Listeners)
    {
        listener.Invoeritem = null;
    }
    Listeners.Clear();
}

By the way: in this case you should make the listeners inverse. Don't forget to map it to the same foreign key.