linq select

var categoryIdArray = MusicCategoryRelationBLL.GetModel(music.Id);
            music.MusicCategoryIds = string.Empty;
            //if (categoryIdArray.Count > 0)
            //{
            //    foreach (var item in categoryIdArray)
            //    {
            //        music.MusicCategoryIds += "," + item.Id;
            //    }
            //    music.MusicCategoryIds = music.MusicCategoryIds.Substring(1);
            //}
            //var result = categoryIdArray.AsEnumerable().Select(n => new { Id = (n.Id).ToString() }).ToArray();
            var result = categoryIdArray.AsEnumerable().Select(n => (n.Id).ToString()).ToList();

var result = categoryIdArray.AsEnumerable().Select(n => (n.Id).ToString());

var result = categoryIdArray.Select(n => (n.Id).ToString());

music.MusicCategoryIds = string.Join(",", result);