Question

I have 2 classes that implment an interface.
The interface is passed into a method as a parameter, and subsequently used as the T class in the following NHibernate syntax

Session.Query<T>() 

However, as the interface is implemented by 2 classes, the SQL that gets run by Session.Query is 2 Select statements (Select .. from Boy. and Select .. from Girl).

What I need to know is how to “convert” the IChild parameter into a Class, and then use that Class to populate the Session.Query() call.

The code is below. As you can see I have a workaround, but it’s not pretty and with multiple IChild classes will become a mass of duplicated code.

Thanks!

public interface IChild
{
    DateTime Date { get; }
    Parent Parent { get; set; }
}

public class Boy : IChild
{
    public virtual Parent Parent { get; set; }
    public virtual DateTime GraduationDate { get; set; }
    public virtual DateTime Date { get { return GraduationDate; } set { } }
}

public class Girl : IChild
{
    public virtual Parent Parent { get; set; }
    public virtual DateTime WeddingDate { get; set; }
    public virtual DateTime Date { get { return WeddingDate; } set { } }
}

    public bool Create(IChild entity)
    {            
        //Is there an existing child record for the key details
        IChild child = null;
        if(entity is Boy)
        {
            child = Session.Query<Boy>()
                .Where(x => x.Date == entity.Date)
                .SingleOrDefault();
        }
        else if (entity is Girl)
        {
            child = Session.Query<Girl>()
                .Where(x => x.Date == entity.Date)
                .SingleOrDefault();
        }

    return child.Parent != null;            
    }

Answer 1

Use generics:

public bool Create<T>(T entity)
where t : class, IChild
{            
    //Is there an existing child record for the key details
    IChild child = null;
        child = Session.Query<T>()
            .Where(x => x.Date == entity.Date)
            .SingleOrDefault();

return child.Parent != null;            
}