using Npgsql;
using NpgsqlTypes;
using System;
using System.Data;

namespace NPgSqlTest
{
  class Program
  {

/*

-- object definitions in the database

CREATE TYPE xy
       AS (x real,
           y real);

CREATE FUNCTION public.fxy(_xy xy)
                RETURNS real
AS
$$
BEGIN
  RETURN _xy.x + _xy.y;
END;
$$
LANGUAGE plpgsql;
*/

    public class XY
    {
      public float x;
      public float y;
      public XY()
      {

      }
    }

    static int Main(string[] args)
    {
      NpgsqlConnection.MapCompositeGlobally<XY>("public.xy");
      try
      {
        using (NpgsqlConnection connection = new NpgsqlConnection("Host=*; Port=*; Database=*; Username=*; password=*;"))
        {

          connection.Open();

          using (NpgsqlCommand command = connection.CreateCommand())
          {
            command.CommandType = CommandType.StoredProcedure;
            command.CommandText = "fxy";
            NpgsqlParameter parameter = new NpgsqlParameter("_xy", NpgsqlDbType.Composite);
            XY xy = new XY();
            xy.x = 7;
            xy.y = 10;
            parameter.Value = xy;
            // commenting the following line out I get the exception
            // when I uncomment it, the exception is gone and everythings works fine
            //parameter.SpecificType = typeof(XY);
            command.Parameters.Add(parameter);
            Console.Out.WriteLine(command.ExecuteScalar());
          }
        }
      }
      catch (Exception exception)
      {
        Console.Error.WriteLine(exception);
        Console.Error.WriteLine();
      }

      Console.Out.WriteLine("DONE");
      Console.In.Read();
      return 0;
    }
  }
}