Hey guys,

I'm trying to understand cascades a little bit, and I seem to have run into a snag of sorts. I'm using NHibernate 1.0.0.

This is a sample hbm file for what I'm trying to do:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="BiaCreations.Core.Planet, BiaCreations.Core" table="Planets">

<cache usage="read-write" />

<id name="Id" column="PlanetId" type="Int32" unsaved-value="-1">
<generator class="native">
<param name="sequence">pm_planet_planetid_seq</param>
</generator>
</id>
<property name="Name" column="Name" type="string" length="64" />

<bag name="People" inverse="true" cascade="delete" lazy="true">
<cache usage="read-write" />
<key column="PlanetId" />
<one-to-many class="BiaCreations.Core.Person, BiaCreations.Core" />
</bag>
</class>

<class name="BiaCreations.Core.Person, BiaCreations.Core" table="People">

<cache usage="read-write" />

<id name="Id" column="PersonId" type="Int32" unsaved-value="-1">
<generator class="native">
<param name="sequence">pm_person_personid_seq</param>
</generator>
</id>
<property name="Name" column="Name" type="string" length="64" />

<many-to-one cascade="save-update"
name="Planet"
class="BiaCreations.Core.Planet, BiaCreations.Core"
column="PlanetId"
not-null="true"
/>

<bag name="Items" inverse="true" cascade="delete" lazy="true">
<cache usage="read-write" />
<key column="PersonId" />
<one-to-many class="BiaCreations.Core.Item, BiaCreations.Core" />
</bag>
</class>

<class name="BiaCreations.Core.Item, BiaCreations.Core" table="Items">

<cache usage="read-write" />

<id name="Id" column="ItemId" type="Int32" unsaved-value="-1">
<generator class="native">
<param name="sequence">pm_item_itemid_seq</param>
</generator>
</id>
<property name="Name" column="Name" type="string" length="64" />

<many-to-one cascade="save-update"
name="Person"
class="BiaCreations.Core.Person, BiaCreations.Core"
column="PersonId"
not-null="true"
/>
</class>
</hibernate-mapping>

__________________

Now in code, say I have a Planet object that has a couple Person objects in it's People collection. If I create a new Item, I would think that both the Person object and Planet object would be updated because of the cascade options that I specified.

That doesn't seem to be the case, though. I'm seeing the Person object being updated, but the Planet object doesn't seem to be. It contains an old version of the Person object in the People collection.

Am I doing something wrong or is this a limitation with cascading?

If you need more info, please let me know.

Thanks

Jim

I think a code example would help here because it's a bit hard to understand what you are doing and what results you are expecting to get from a plain text description.

In particular, what is "an old version of the Person object" that Planet contains? Old compared to what? And why do you expect objects to change somehow just because you created another object?

I was hoping that because I had cascade="save-update" specified on the one-to-many relationships, when that object was updated, it's related object's would be updated also. Maybe I'm asking too much, though :)

I know that there are better ways of doing what I'm outlining below, but it should provide an example of how I'm using the objects.

ISession session = SessionFactory.Instance.NHibernateFactory.OpenSession();

Planet planet = session.Load(typeof(Planet), 1) as Planet;

Person person = planet.People[0] as Person;

Item item = new Item();
item.Person = person;
item.Name = "Sample";

ITransaction trn = session.BeginTransaction();
try
{
session.Save(item);
trn.Commit();
}
catch (Exception)
{
trn.Rollback();
throw;
}

planet = session.Load(typeof(Planet), 1) as Planet;

// At this point, the person object has the correct Items count, but the
// collection on the planet object has not been updated with the new copy
// of the person object.

int itemCount = 0;
foreach (Person p in planet.People)
{
itemCount += p.Items.Count;
}


session.Close();
session.Dispose();

Doing work in two sessions in parallel in this way isn't really a good idea. You should remember that a session assumes it's running within one (logical) transaction and thus caches the objects associated with it, so your second Load call returns exactly the same object as the first one and doesn't go to the database at all, this may be the reason why it's unaware of changes.

Hrm... ok. I guess I just figured that the cascade for save-update would continue up along the object model like the cascade for delete does for bags. Thanks for your help.
[/code]

Out of curiosity, is there a way that I can trick nHibernate into thinking that the collection (on the planet object) hasn't been returned from the db (isn't cached)? Like if I set the collection property to null or something similar...