var tags = from tag in db.File_Tag select tag;
                        foreach (var item in tags)
                        {
                            if (item.TagPath==null)
                            {
                                string fileId = item.Id.ToString();
                                Guid? thisId=item.ParentId;
                                bool istrue = true;
                                do
                                {
                                    var _lists = from tag in tags where tag.Id == thisId select tag;
                                    if (_lists.Count()>0)
                                    {
                                        foreach (var i in _lists)
                                        {
                                            fileId = i.Id.ToString() + "/" + fileId;
                                            thisId = i.ParentId;
                                        }
                                    }
                                    else
                                    {
                                        istrue = false;
                                    }
                                } while (istrue);

                                item.TagPath = fileId;
                                
                            }
                        }