NHibernate: Removing child from many-to-many relationship causes exception

Question

I've been battling with this issue for a couple of days now.

I have a couple of classes in a many-to-many relationship, configured like so:

<class name="Entry" table="Entries">
    <id name="Id" column="Id">
      <generator class="native" />
    </id>
    <timestamp name="LastUpdated" column="Entry_LastUpdated" generated="always" />
    ...
    <bag name="Sections" generic="true" table="EntrySections" inverse="false" cascade="none">
      <key column="EntrySection_EntryId" />
      <many-to-many column="EntrySection_SectionId" class="Blogs.BusinessLogic.Section, Blogs.BusinessLogic"/>
    </bag>
</class>

<class name="Section" table="Sections">
    <id name="Id" column="Id" unsaved-value="0">
      <generator class="native" />
    </id>
    <timestamp .../>
    ...
    <bag name="Entries" generic="true" table="EntrySections" inverse="false" cascade="none">
        <key column="EntrySection_SectionId" />
        <many-to-many column="EntrySection_EntryId" class="Blogs.BusinessLogic.Entry, Blogs.BusinessLogic"/>
    </bag>
</class>

It is configured in a way that I could delete, say, a Section object and its associations to any entries will be removed.

However, when I wish to only remove the associations, for example:

entry.Sections.Remove(section);

This is the only action I perform on this object. However, when the session flushes, the following StaleObjectStateException exception is thrown:

Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Project.BusinessLogic.Entry#22]

I've been toying with the inverse and cascade values and googling for answers, but cannot find any solution. Neither inverse="true" nor cascade="all/all-delete-orphan" did the trick.
Is this a problem related to the many-to-many relationship, or am I looking in the wrong direction?
Are my classes mapped incorrectly?

Edit

Could this be an issue resulting from the way NHibernate works with the and the DateTime struct?

Can you include your <id> section from each mapping? Are you using <version> at all? — Shane Courtrille
@ShaneC: I've added the <id> section. I'm using a timestamp mapping instead of version. — GeReV

Frederik Gheysels Frederik Gheysels · Accepted Answer · 2010-07-07T12:19:16

Don't you have to mark one end of the association as 'inverse=true' and the other as 'inverse=false' ? By doing so, you define the 'owner' of the association.

NHibernate: Removing child from many-to-many relationship causes exception

2 Answers