Problem when getting an entity which has been modified in another session

Question

Hello all,

I have a strange problem in my rich client application. Here is some background:

• I use one session per view model.
• My view models communicate with each others with a Mediator.

I have a management view model where I display a list of my entities. I can edit an entity, which results in the opening of a new view model, which receives the id of the entity to be edited through the mediator.

When the user clicks on the Edit button, my edit view model updates the entity with its own session, and uses the Mediator again, with the edited entity id, to ask the main view model to refresh the list of the entities.

Let's say I change a boolean property called Visible, on the entity.

When I edit the entity, I can see an UPDATE call to NHibernate, updating the entity in the database.

When I come back in the main view model, I do 2 things :

1. I ask from NHibernate the updated entity
2. I refresh the list of the entities, to display all the entities, with a custom filter. (Display all the visible entities for example.)

What's weird is that the entity I get from NH in the first instruction has still the old value of the Visible property, but in the list of my visible entities, the entity I've edited is not present...

Here is the two functions of the repository I use to respectively get the entity and get the list of all the visible entities:

public virtual TEntity Get(int id)
{
    return Session.Get<TEntity>(id);
}

public IEnumerable<Player> GetAllPlayersSortedByLastName(bool visible = true)
{
    return from player in Session.Linq<Player>()
            where player.Visible == visible
            orderby player.LastName
            select player;
}

What's wrong with my code? Why doesn't the entity I get back from NH in my main view model after it has been edited doesn't have the correct values?

Thanks in advance

Answer 1

You keep the ISession alive during the life-time of each ViewModel?

If that is the case - the Entity is present in the MainViewModel's ISession's IdentityMap - so when you ask it to refresh - it just grabs the one in the IdentityMap.

You need to ISession.Evict(updatedEntity) and then run your query again.

This is the whole idea of the 1st level cache in the ISession (to not hit the database if it has been previously loaded.

If you do not want this behaviour and want to bypass the first level cache - you can either open a child session from the session - or run in a IStatelessSession.