Question

I am trying to locate duplicate objects based on 2 fields but ONLY where a 3rd field is also null

ItemNumber, Name, Pricebook, Parent
Item1, A, B, <null>
Item2, A, B, Item1
Item3, A, B, <null>
Item4, A, B, Item1
Item5, A, B, Item2

So in the above list the only 2 duplicate items are effectively Item1 and Item3

var duplicateItemsList =
    from i in items
    group i by new { i.ItemNumber, i.Pricebook, i.Parent } into d
    where d.Count() > 1
    select new { ItemNumber = d.Key.ItemNumber, Pricebook = d.Key.Pricebook, Parent = d.Key.Parent, Count = d.Count() };

The trouble I am having is working the check for the null field value in the Linq query.

After the above Linq query I just want to end up with a list containing the duplicated ItemNumber and Pricebook field values.

Answer 1

I don’t think you need Parent property in result and in groping key, because it will have null value. Also you don’t need to specify property name for anonymous object if it is same as name of assigned property.

var duplicateItemsList =
    from i in items
    where i.Parent == null
    group i by new { i.Name, i.Pricebook } into d
    where d.Count() > 1
    select new { 
                  d.Key.Name, 
                  d.Key.Pricebook, 
                  Count = d.Count()
               };

Also you can introduce new range variable to store items count in group. Then items count will be calculated only once:

var duplicateItemsList =
    from i in items
    where i.Parent == null
    group i by new { i.Name, i.Pricebook } into d
    let groupItemsCount = d.Count()
    where groupItemsCount > 1
    select new { 
                  d.Key.Name, 
                  d.Key.Pricebook, 
                  Count = groupItemsCount
               };

UPDATE as @Blachshma pointed, you have grouping by ItemNumber instead of Name