Nullable int not working as expected in LINQ (C#)

Question

The following works as expected (LINQ to Entities):

var topics = (from t in ctx.Topics where t.SubjectId == subjectId && t.ParentId == null select new { t.Title, t.Id }).ToList();

However, the following returns nothing:

int? parent = null;
var topics = (from t in ctx.Topics where t.SubjectId == subjectId && t.ParentId == parent select new { t.Title, t.Id }).ToList();

Topic.ParentId is a nullable int. It's easy to work around, but this puzzles me. Can anyone shed any light?

Same question here: http://stackoverflow.com/questions/682429/how-can-i-query-for-null-values-in-entity-framework/4262617#4262617 — Slauma, Apr 12 '11 at 18:58

score 4 · Accepted Answer · answered Apr 12 '11 at 18:50

4

You are definately not the first person to observe this... interesting... behavior.

In short, it's difficult to handle different ways of expressing null.

answered Apr 12 '11 at 18:50

Thebigcheeze

1

Thank you. From the link in your answer, I found an easy workaround: t.ParentId.Equals(parent). But how strange! I'm glad it's not just me going crazy! – James Apr 12 '11 at 18:59
@James, I though this work around only works for Linq to SQL and not Linq to Entities... Did it work for Linq to Entities for you? – Andrew Savinykh Apr 13 '11 at 04:44
@zespri No, I posted too soon! It works when parent is null, but not in other cases. I ended up with if (parent==null) ... – James Apr 13 '11 at 16:49

1 Answers1