//通过父节点找到所有子节点

        public IEnumerable<ModelInfo> GetSonID(string p_id)

        {

            var query = from c in _context.Model_Info

                        where c.parent_dbId == p_id

                        select c;

            return query.ToList().Concat(query.ToList().SelectMany(t => GetSonID(t.object_id)));

        }