Question

I am having some trouble with a linq query

var matches = from po in purchaseOrders
          from poItem in po.Items
          where TestMatch(poItem)
          select new Item(poItem);

purchaseOrders is a List
Each PurchaseOrder contains a List

What I need for a result, is the first poItem that matches (based on the result of TestMatch(poItem)) in each purchase order, OR a blank Item object.

So that in the end matches.Count == purchaseOrders.Count

Currently, I only get items that match in a PO, and I’m not sure how to ensure I only get ONE item per PO. And I don’t know how to ensure if there is no match, that I get a blank Item for that PO.

Answer 1

It sounds like you want something like:

 var matches = from po in purchaseOrders
               let poItem = po.Items.FirstOrDefault(item => TestMatch(item))
               select new { PO = po, 
                            Item = poItem == null ? null : new Item(poItem) };

With C# 4 you can use a method group conversion for the argument to FirstOrDefault:

 var matches = from po in purchaseOrders
               let poItem = po.Items.FirstOrDefault(TestMatch(item)
               select new { PO = po, 
                            Item = poItem == null ? null : new Item(poItem) };