Architecture with SQL Server CE

I have to build a number of small independent applications, that can be copied to an USB device and run from there out of the box. So I was thinking to use WPF, that uses EF code first to connect to a SQL Server CE database.

My question is about what architecture I should use. Although the apps are standalone, I would still like to decouple UI from domain from data, to have a clean separation of layers. But I also don't want to make it too complex.

So, I want to have a UI layer (WPF/MVVM) that uses the underlying domain layer (domain objects with domain logic) and repositories (that use EF code first).

My question is: what pattern should I use to make EF work in this case? Is there somewhere an example that demonstrates how to implement CRUD operations in such scenario? For exampl开发者_如何学Pythone, should I create one context and leave it open; or should I implement the unit of work pattern and attach objects to other context if needed?

Or would you do it in a totally different way?

Thanks for the advice!

---

The EF context should be open for as short time as possible. Preferably use it within a using statement.

private static void ApplyItemUpdates(SalesOrderDetail originalItem,
    SalesOrderDetail updatedItem)
{
    using (AdventureWorksEntities context =
        new AdventureWorksEntities())
    {
        context.SalesOrderDetails.Attach(updatedItem);
        // Check if the ID is 0, if it is the item is new. 
        // In this case we need to chage the state to Added.
        if (updatedItem.SalesOrderDetailID == 0)
        {
            // Because the ID is generated by the database we do not need to
            // set updatedItem.SalesOrderDetailID.
            context.ObjectStateManager.ChangeObjectState(updatedItem, System.Data.EntityState.Added);
        }
        else
        {
            // If the SalesOrderDetailID is not 0, then the item is not new
            // and needs to be updated. Because we already added the 
            // updated object to the context we need to apply the original values.
            // If we attached originalItem to the context 
            // we would need to apply the current values:
            // context.ApplyCurrentValues("SalesOrderDetails", updatedItem);
            // Applying current or original values, changes the state 
            // of the attached object to Modified.
            context.ApplyOriginalValues("SalesOrderDetails", originalItem);
        }
        context.SaveChanges();
    }
}

There is a method called Attach, which attachs entities to a context:

private static void AttachRelatedObjects(
    ObjectContext currentContext,
    SalesOrderHeader detachedOrder,
    List<SalesOrderDetail> detachedItems)
{
    // Attach the root detachedOrder object to the supplied context.
    currentContext.Attach(detachedOrder);

    // Attach each detachedItem to the context, and define each relationship
    // by attaching the attached SalesOrderDetail object to the EntityCollection on 
    // the SalesOrderDetail navigation property of the now attached detachedOrder.
    foreach (SalesOrderDetail item in detachedItems)
    {
        currentContext.Attach(item);
        detachedOrder.SalesOrderDetails.Attach(item);
    }
}

http://msdn.microsoft.com/en-us/library/bb896271.aspx