Question

I have two objects – ContentPage, which has a collection of ChildLinks.

ContentPage
-----------
ID
Title

ChildLink
----------
ID
ParentPageID [ContentPage]
ChildPageID [ContentPage]
Priority

The ContentPage.ChildLinks property utilises the 2nd level cache. I am using Fluent NH to configure Nhibernate, and using Nhibernate 3.1. Cache is set as ‘Read-Write’ both for the collection, and the ‘ChildLink’ class.

I’ve noticed that whenever I delete a ChildLink, the collection cache is not being invalidated. Thus, when I call the ContentPage.ChildLinks, I get an error:

no row with the given identifier exists

I’ve turned off the cache, and it works well. Shouldn’t the cache be automatically invalidated? I am using SysCache as the cache provider, and MySQL as the database.

Thanks in advance!

Answer 1

I had the same problem and I can across the following article which solved my problem:

Inverse Mapped Collections and NHibernate’s Second-Level Cache

Basically if you have mapped your collections as inverse, when you delete the child item you also have to make sure to explicitly remove it from the parent collection or the cache state will be invalid after you delete the child. The first thing to check is if the relationship really needs to be inverse.

Assuming inverse is necessary or desired, and using your example:

Instead of only something like:

Session.Delete(ChildLink);

You have to do:

ContentPage.ChildLinks.Remove(ChildLink);
ChildLink.ParentPage = null;
Session.Delete(ChildLink);

You also might need to explicitly save your ContentPage object at this point as well, it depends on your Session flush settings.

I use methods on my entities for managing such inverse relationships, for example:

public ChildLink
{
    public ContentPage ParentPage {get;set;}

    public void AddToPage(ContentPage addTo)
    {
        addTo.ChildLinks.Add(this);
        this.ParentPage = addTo;
    }

    public void RemoveFromPage()
    {
        ParentPage.ChildLinks.Remove(this);
        this.ParentPage = null;
    }

}

And then when deleting a child object:

ChildLink.RemoveFromPage();
Session.Delete(ChildLink);