Question

Having trouble with an HQL query. If I remove the avg(..) from it it will return all of the empty weights, so the trouble is with the avg function. It seems clear in the Nhibernate docs that I can perform an aggregate function on the select item like this. Is my problem something to do with query.ToList not liking to return a list of one thing? I just get the “Could not execute query[SQL:SQL not available] message.

 public List<T> HQLQuery<T>(string HQL) //in UnitOfWork
    {
        var query = session.CreateQuery(HQL);
        return query.List<T>().ToList<T>();


    }

   public static float estimateTruckEmptyWeight(int vehicleID)
    {
        UnitOfWork uow = new UnitOfWork();
        List<float> results = uow.HQLQuery<float>("select avg(ev.EmptyWeight) from FieldSystemCore.Domain.EmptyVehicle ev where ev.Vehicle.ID = '" + vehicleID + "'");
        return results[0];

    }

Answer 1

The trouble turned out to be because avg returns double in Nhibernate, not float.

I wish the exception gave me a clue that this was the case.