public IHttpActionResult Create(Instance instance)
        {
            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            Context.Instances.Add(instance);
            Context.SaveChanges();

            return Ok();
        }
        public IHttpActionResult Update(int id, Instance instance)
        {
            instance.Id = id;

            if (!ModelState.IsValid)
            {
                return BadRequest(ModelState);
            }

            Context.Instances.Attach(instance);
            var entry = Context.Entry(instance);
            entry.State = EntityState.Modified;

            Context.SaveChanges();

            return Ok();
        }