gistfile1.cs

        // GET api/Poi/GetGolf
        public IEnumerable<myGolf> GetGolf()
        {
           var mypoi = (from xy in db.PoiSet where xy.Primarytype == "golf"
                         select new myGolf 
                         {
                             Id = xy.Id,                             
                             Poiname = xy.Nodename,
                             Region = xy.Region.RID,
                             Ort = xy.Ort.RID,
                             GPSEast = xy.PoiGps.Where(x => x.type == "position").FirstOrDefault().Gps.east,
                             GPSNorth = xy.PoiGps.Where(x => x.type == "position").FirstOrDefault().Gps.north,
                             GolfDetails = xy.PoiDetail.OfType<Golf>()
                         });     

            if (mypoi == null)
            {
                throw new HttpResponseException(Request.CreateResponse(HttpStatusCode.NotFound));
            }

            return mypoi;
        }
                         
    //Custom class                     
    public class myGolf 
    {
        public int Id { get; set; }

        public string Poiname { get; set; }        
        public string Region { get; set; }
        public string Ort { get; set; }
        public string GPSEast { get; set; }
        public string GPSNorth { get; set; }

        public IEnumerable<Golf> GolfDetails { get; set; }
    }