Can you see NHibernate results mid-query during debugging in Visual Studio?

Question

Having been comfortably using Entity Framework for many years, I've just been thrown in the deep end with a project that uses NHibernate and I'm really struggling. The documentation is sparse and unhelpful if you're working with it for the first time, and most tutorial and example sites are out of date - I understand it changed significantly in v3?

Normally, I learn things best when trying to work with them, so I jumped in and tried to see what I could do. But I've hit a bug in this pre-existing function (none of this code is mine):

public IDictionary<long, string> GetSeriesFilterData(string userId)
{
    Series seriesAlias = null;
    Event eventAlias = null;
    Session sessionAlias = null;
    Dealership dealershipAlias = null;

    var query = _repository.Session.QueryOver(() => seriesAlias)
        .Where(() => !seriesAlias.IsArchived);

    var dealershipIds = QueryOver.Of<ApplicationUserDealership>()
        .Where(x => x.ApplicationUser_Key == userId)
        .SelectList(list => list.SelectGroup(x => x.Dealership_Id));

    dealershipIds.Where(x => x.Dealership_Id == dealershipAlias.Id);
    query
        .JoinAlias(() => sessionAlias.Dealership, () => dealershipAlias, JoinType.LeftOuterJoin)
        .WithSubquery.WhereExists(dealershipIds);


    var results = query.SelectList(x => x
            .SelectGroup(() => seriesAlias.Id)
            .SelectGroup(() => seriesAlias.Name))
        .List<object[]>()
        .ToDictionary(x => (long) x[0], x => (string) x[1]);

    return results;
}

The exception, thrown when collecting the result, is:

An exception of type 'NHibernate.QueryException' occurred in NHibernate.dll but was not handled in user code

Additional information: could not resolve property: sessionAlias

My suspicion is that this is because dealershipIds is empty, but I'm struggling to prove that this is the case. Working with Entity Framework, it's possible to see the results of a query during debugging by unpacking its object graph. However, I can't seem to do that in NHibernate.

Is it possible to see the results of a query fragment via debugging, or do I have to pull it out with a Select statement?

Answer 1

The QueryOver you've posted seems to be missing the part where the sessionAlias alias is assigned to something.

As it's being done for the others (except eventAlias which seems completely unused) the alias needs to be assigned to a property/path on the entity class being queried via JoinAlias/JoinQueryOver or to the entity itself as it's done on the QueryOver creation with seriesAlias.

Then, that alias (variable) can be used in Where, OrderBy, etc.

For example, supposing that Session is an entity referenced from a property of Series (no clue regarding your actual entity model) the following would fix your problem as it will bind sessionAlias to that property:

// This binds the alias to the property.
query.JoinAlias(s => s.Session, () => sessionAlias);

// This is the same as above, but uses the previously defined alias for the main entity, 
// just to show how aliases can be used.
query.JoinAlias(() => seriesAlias.Session, () => sessionAlias);