public RelatedCatalogItemsViewModel GetRelationshipsFromItem(Item catalogItem, Rendering rendering)
        {
            if (catalogItem == null || !catalogItem.IsDerived(Foundation.Commerce.Templates.Commerce.CatalogItem.Id) || !catalogItem.FieldHasValue(Foundation.Commerce.Templates.Commerce.CatalogItem.Fields.RelationshipList))
            {
                return(null);
            }

            RelationshipField field = catalogItem.Fields[Foundation.Commerce.Templates.Commerce.CatalogItem.Fields.RelationshipList];

            var model = new RelatedCatalogItemsViewModel();
            var productRelationshipInfoList = field.GetRelationships();

            productRelationshipInfoList = productRelationshipInfoList.OrderBy(x => x.Rank);
            var productModelList = GroupRelationshipsByDescription(productRelationshipInfoList);

            model.RelatedProducts.AddRange(productModelList);

            return(model);
        }
        /// <summary>
        /// Gets a lists of target items from a relationship field
        /// </summary>
        /// <param name="storefront">The storefront.</param>
        /// <param name="visitorContext">The visitor context.</param>
        /// <param name="field">the relationship field</param>
        /// <param name="rendering">The target renering.</param>
        /// <param name="relationshipNames">the names of the relationships, to retrieve (for example upsell).</param>
        /// <returns>
        /// a list of relationship targets or null if no items found
        /// </returns>
        public RelatedCatalogItemsViewModel GetRelationshipsFromField([NotNull] CommerceStorefront storefront, [NotNull] VisitorContext visitorContext, RelationshipField field, Rendering rendering, IEnumerable <string> relationshipNames)
        {
            Assert.ArgumentNotNull(storefront, "storefront");

            relationshipNames = relationshipNames ?? Enumerable.Empty <string>();
            relationshipNames = relationshipNames.Select(s => s.Trim());
            var model = new RelatedCatalogItemsViewModel();

            if (field != null)
            {
                var productRelationshipInfoList = field.GetRelationships();
                productRelationshipInfoList = productRelationshipInfoList.OrderBy(x => x.Rank);
                var productModelList = this.GroupRelationshipsByDescription(storefront, visitorContext, field, relationshipNames, productRelationshipInfoList, rendering);
                model.RelatedProducts.AddRange(productModelList);
            }

            model.Initialize(rendering);

            return(model);
        }