public ImageVo insert(ImageVo input)
        {
            using (var db = new MainDb())
            {

                db.images.Add(input);
                db.SaveChanges();

                return input;
            }
        }
        public ImageVo update(ImageVo input, Guid? imageId= null)
        {
            using (var db = new MainDb())
            {

                if (imageId == null)
                    imageId = input.imageId;

                var res = db.images.FirstOrDefault(e => e.imageId == imageId);

                if (res == null) return null;

                input.created = res.created;
               // input.createdBy = res.createdBy;
                db.Entry(res).CurrentValues.SetValues(input);

                db.SaveChanges();
                return res;

            }
        }