var _products_lookup1 = _Products.ToLookup(o=> o.CategoryID);
				var _category_dict = _Categories.ToDictionary(c => c.CategoryID);
				var _products_lookup2 = _Products.ToLookup(a=> a.SupplierID);
				var _supplier_dict = Suppliers.ToDictionary(b=> b.SupplierID);

				foreach (var o in _Products) o.Category = _customers_dict[o.CustomerID];
				foreach (var c in _Categories) c.Products = _products_lookup1[c.CategoryID];
				foreach (var a in _Products) a.Supplier = _supplier_dict[a.SupplierID];
				foreach (var b in _Suppliers) b.Suppliers = _products_lookup2[b.SupplierID];