API for Multi Vendor

IList<int> alreadyFilteredSpecOptionIds = model.PagingFilteringContext.SpecificationFilter.GetAlreadyFilteredSpecOptionIds(_webHelper);

 public virtual List<int> GetAlreadyFilteredSpecOptionIds(IWebHelper webHelper)
            {
                var result = new List<int>();

                var alreadyFilteredSpecsStr = webHelper.QueryString<string>(QUERYSTRINGPARAM);
                if (String.IsNullOrWhiteSpace(alreadyFilteredSpecsStr))
                    return result;

                foreach (var spec in alreadyFilteredSpecsStr.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
                {
                    int specId;
                    int.TryParse(spec.Trim(), out specId);
                    if (!result.Contains(specId))
                        result.Add(specId);
                }
                return result;
            }