Question

I am working with an NHibernate project that has a method that returns an IQuery object.
I want to find the oldest car with a particular colour.

At the moment it returns the oldest car only if you if you specify the colour correctly (or don’t specify it at all).

I can see roughly what I am doing wrong (I am getting the maxAge for the whole table and then adding it as a restriction on the existing IQueryOver).

How do I change the code to get the max age just for existing IQueryOver?

private IQueryOver GetFilteredQuery()
{
    var query = Session.QueryOver<Car>();

    if (this.Colour != nulI)
    {
        query.Where(x => x.Colour == this.Colour));
    }

    if (this.GetOldestCar == true)
    {
        QueryOver<Car> maxAge= QueryOver.Of<Car>()
            .SelectList(c => c.SelectMax(x => x.Age));

        query.Where(Subqueries.WhereProperty<Car>(i => i.Age).Eq(maxAge));
    }

    return query;
}

Answer 1

To get the oldest Car, you may try :

var query = Session.QueryOver<Car>().OrderBy(x=>x.Age).Desc().Take(1);

This would lead to :

private IQueryOver GetFilteredQuery()
{
    var query = Session.QueryOver<Car>();

    if (this.Colour != null)
    {
        query.Where(x => x.Colour == this.Colour));
    }

    if (this.GetOldestCar)
    {
        query.OrderBy(x=>x.Age).Desc().Take(1)
    }

    return query;
}