public IHttpActionResult Index()
        {
            try
            {
                var ad      = new AdsService();
                var adverts = ad.DisplayAllAds().ToList();

                List <AdvertisementViewModel> advertisements = new List <AdvertisementViewModel>();
                foreach (var item in adverts)
                {
                    advertisements.Add(new AdvertisementViewModel()
                    {
                        Id              = item.Id,
                        Title           = item.Title,
                        Description     = item.Description,
                        Location        = item.Location,
                        MinSellingPrice = item.MinSellingPrice,
                        MaxSellingPrice = item.MaxSellingPrice,
                        CreationDate    = item.CreationDate,
                        ExpirationDate  = item.ExpirationDate
                    });
                }
                if (advertisements != null)
                {
                    return(Ok(advertisements));
                }
            }
            catch (Exception ex)
            {
                throw new OnlineAdsAppException("The ads cannot be displayed");
            }
            return(InternalServerError());
        }