Delete throws "deleted object would be re-saved by cascade"

Question

I have following model:

<class name="Person" table="Person" optimistic-lock="version">
  <id name="Id" type="Int32" unsaved-value="0">
    <generator class="native" />
  </id>
  <!-- plus some properties here -->
</class>

<class name="Event" table="Event" optimistic-lock="version">
  <id name="Id" type="Int32" unsaved-value="0">
    <generator class="native" />
  </id>
  <!-- plus some properties here -->
</class>

<class name="PersonEventRegistration" table="PersonEventRegistration" optimistic-lock="version">
  <id name="Id" type="Int32" unsaved-value="0">
    <generator class="native" />
  </id>
  <property name="IsComplete" type="Boolean" not-null="true" />
  <property name="RegistrationDate" type="DateTime" not-null="true" />
  <many-to-one name="Person" class="Person" column="PersonId" foreign-key="FK_PersonEvent_PersonId" cascade="all-delete-orphan" />
  <many-to-one name="Event" class="Event" column="EventId" foreign-key="FK_PersonEvent_EventId" cascade="all-delete-orphan" />
</class>

There are no properties pointing to PersonEventRegistration either in Person nor in Event.

When I try to delete an entry from PersonEventRegistration, I get the following error:

"deleted object would be re-saved by cascade"

The problem is, I don't store this object in any other collection - the delete code looks like this:

public bool UnregisterFromEvent(Person person, Event entry)
{
    var registrationEntry = this.session
        .CreateCriteria<PersonEventRegistration>()
        .Add(Restrictions.Eq("Person", person))
        .Add(Restrictions.Eq("Event", entry))
        .Add(Restrictions.Eq("IsComplete", false))
        .UniqueResult<PersonEventRegistration>();

    bool result = false;
    if (null != registrationEntry)
    {
        using (ITransaction tx = this.session.BeginTransaction())
        {
            this.session.Delete(registrationEntry);
            tx.Commit();
            result = true;
        }
    }
    return result;
}

What am I doing wrong here?

Answer 1

As far as I know, cascade="all-delete-orphan" belongs on the collection mapping element, not the many-to-one. You haven't shown the other two parts of your mapping so I can't say for sure but this is possible (likely) the problem.

I think Person should look something like:

<!-- other properties -->
<set name="Events" inverse="true" cascade="all-delete-orphan">
    <key column="Person_id" />
    <one-to-many class="PersonEventRegistration" />
</set>

Event:

<!-- similar mapping for Event -->

PersonEventRegistration:

<!-- other properties -->
<many-to-one name="Person" class="Person" column="PersonId" foreign-key="FK_PersonEvent_PersonId" cascade="delete" <!-- or many ="all" ? --> />

Actually, the above could be conflicting cascades (which might be what you have). So really, my answer is two things:

1. cascade="all-delete-orphan" has no meaning on many-to-one.
2. Make sure you have really thought-through how you are working with your entities and how they should cascade their operations.