Hello it seems that you have re-written the GetLowStockProductCombinations, but you forgot to put some (). In terms of .net code the stuff is ok, but since it;s translated to sql it's bad.
Put some () for the || conditions or it will return all products :)
In sql it's translated to this
(([pac].[StockQuantity] < [pac].[NotifyAdminForQuantityBelow] AND [p].[ManageInventoryMethodId] = 2 AND 1 <> [p].[Deleted] AND [p].[ProductTypeId] <> 10 OR [p].[VendorId] = @vendorId) OR [p].[Published] IS NULL)
Corrected below:
var combinations = from pac in _productAttributeCombinationRepository.Table
join p in _productRepository.Table on pac.ProductId equals p.Id
where
//filter by combinations with stock quantity less than the minimum
pac.StockQuantity < pac.NotifyAdminForQuantityBelow &&
//filter by products with tracking inventory by attributes
p.ManageInventoryMethodId == (int)ManageInventoryMethod.ManageStockByAttributes &&
//ignore deleted products
!p.Deleted &&
//ignore grouped products
p.ProductTypeId != (int)ProductType.GroupedProduct &&
//filter by vendor
((vendorId ?? 0) == 0 || p.VendorId == vendorId) &&
//whether to load published products only
(loadPublishedOnly == null || p.Published == loadPublishedOnly)
orderby pac.ProductId, pac.Id
select pac;
