How do I Insert or Update (or overwrite) a record using NHibernate?

Question

I need to write a row to the database regardless of whether it already exists or not. Before using NHibernate this was done with a stored procedure. The procedure would attempt

Answer 1

I`m using

    public IList GetByExample(T exampleInstance)
    {
        return _session.CreateCriteria(typeof(T))
                    .Add(Example.Create(exampleInstance))
                    .List();
    }

    public void InsertOrUpdate(T target)
    {
        ITransaction transaction = _session.BeginTransaction();
        try
        {
            var res=GetByExample(target);
            if( res!=null && res.Count>0 )
                _session.SaveOrUpdate(target);
            else
               _session.Save(target); 
            transaction.Commit();
        }
        catch (Exception)
        {
            transaction.Rollback();
            throw;
        }
        finally
        {
            transaction.Dispose();
        }
    }

but FindByExample method returns all objects alike not objects with the exact ID what do you suggest ? since I have only object as parameter I don't have access to its specific ID field so I cannot use session.get(Object.class(), id);