Problems casting PersistentGenericBag to List

lucashungaro · **Posted:** Tue May 15, 2007 8:16 pm

NHibernate version: 1.2.0

Full stack trace of any exception that occurs:
Unable to cast object of type
'NHibernate.Collection.Generic.PersistentGenericBag`1[Projeto.Core.Domain.Armazem]' to
type 'System.Collections.Generic.List`1[Projeto.Core.Domain.Armazem]'

Name and version of the database you are using: SQL Server 2005

I have a typed collection and and trying to make it receive a list of persistent entities (mapped as a bag) but I'm getting the error mentioned above.

The error occurs on the following code:

Code:

    private List<Armazem> _armazens;

    public IList<Armazem> Armazens
    {
        set 
        {
            _armazens = (List<Armazem>)value;

        }
   }

called by:

Code:

   Usuario usuario = usuarioDao.GetById(codigoUsuario, false);

   view.Armazens = usuario.Armazens;

Excerpt from the Usuario entity mapping:

Code:

<bag name="Armazens" inverse="false" table="usuario_armazem" lazy="true" cascade="delete">
   <key column="usu_id" />
   <many-to-many class="Projeto.Core.Domain.Armazem,Projeto.Core">
      <column name="arm_id" />
   </many-to-many>
</bag>  

Thanks for any help.

sergey · **Posted:** Wed May 16, 2007 1:04 am

What led you to believe that PersistentGenericBag inherits from list? It doesn't.

lucashungaro · **Posted:** Wed May 16, 2007 8:54 am

Actually, nothing led me into it. I know it doesn't inherits from list.

The problem is: I have this many-to-many relationship mapped as a bag which, as pointed in the documentation, maps to a List. In the entity class the field is declared as an IList and all works well (for testing purposes I changed it to another type of collection and the application failed to initialize).

So, the mapping is correct, the bag is represented as a List in the entity class but how can I access its values? I need to pass the collection to another layer and I'm sure I cannot (or shouldn't) leak NHibernate references through this layer just to use it's generic lists (also, the documentation clearly says not to do that).

Am I missing something?

lucashungaro · **Posted:** Wed May 16, 2007 4:21 pm

Well, simplifying: how can I access the entities of a bag mapping? I can't use a .NET collection?

anortham · **Joined:** Fri Jul 14, 2006 1:51 pm **Posts:** 27

Why do you need to cast to a generic list? Just do this:

Code:

private IList<Armazen> _armazens;

public IList<Armazen> Armazens
{
        set
        {
            _armazens = value;

        }
} 

assuming that view.Armazens is also an IList<Armazen> ...

merge_s.rottem · **Joined:** Tue Aug 23, 2005 5:52 am **Posts:** 335

As a side note, normal best practice is not to provide a setter for collection properties. Get NHibernate to set the underlying field using a field access strategy and only provide a getter for the property.

Cheers,

Symon.

lucashungaro · **Posted:** Wed May 16, 2007 5:47 pm

anortham, merge_s.rottem: this isn't the entity class setter, it's the setter of the _armazens collection of the view object.

I'm using the List collection 'cause I need to use the Find method, which isn't implemented in IList.

IgorK · **Posted:** Thu May 17, 2007 4:17 am

Hi lucashungaro!

You may "wrap" NHibernate collection into BindingList<T> class - either in IList<T> setter (it will hovever ruin lazy capabilities, as BindingList will retreive all collection during construction), either in IList<T> getter - replacing original field with this wrapper - or even via additional property and field (so you'll end with a pair of field/property - one IList<T> for NHibernate and another for your business purposes).