public IHttpActionResult ObservePost(observed_ad obs)
        {
            var exists = db.observed_ad.Any(o => o.ad_id == obs.ad_id && o.user_id == obs.user_id);

            if (exists)
            {
                return(BadRequest("Already observed."));
            }
            else
            {
                var maxId = 1;
                if (db.observed_ad.Any())
                {
                    maxId = db.observed_ad.Max(o => o.observed_id) + 1;
                }
                db.observed_ad.Add(new observed_ad()
                {
                    observed_id = maxId,
                    user_id     = obs.user_id,
                    ad_id       = obs.ad_id
                });
                db.SaveChanges();
                return(Ok("Successfully observed."));
            }
        }
        public IHttpActionResult Delete(int adId, int userId)
        {
            //var ifDelete = db.observed_ad.Any(o => o.ad_id == obs.ad_id && o.user_id == obs.user_id);
            observed_ad toDelete = db.observed_ad.FirstOrDefault(o => o.ad_id == adId && o.user_id == userId);

            if (toDelete != null)
            {
                db.Entry(toDelete).State = System.Data.Entity.EntityState.Deleted;
                db.SaveChanges();
                return(Ok());
            }
            else
            {
                return(BadRequest("No data to delete."));
            }
        }