Linq to Sql - 在where子句中使用sum

I'm trying to select orders that have either over or under 2000 products ordered in them, depending on other values. I need to select the information from the Orders table, but check this value in the OrdersProducts table, specifically the sum of OrdersProducts.ProductQty. I also need to do this using predicate builder, because of other requirements. So far, I have this, but it isn't returning the results correctly. Its using nested Lambda expressions, which I didn't know I could do but I tried it and it works, but its not returning correct results.I'm trying to select orders that have either ov