int? and int comparison when LEFT OUTER JOIN in Linq issue

Question

I am working on a WinForms project which requires to use Linq-To-Sql. I have been able to create my DataContext using the SqlMetal tool, and make s

Answer 1

The first problem was that the property names should be the same as said casperOne♦, but the second problem is that you're comparing a nullable-int, p.child_ID, with a non-nullable-int, t.ID. So you could use the null-coalescing operator in this way:

(int)(p.child_ID ?? default(int))

In this case returns p.child_ID if it isn't null else returns default(int), that is 0.

The query will be:

var query = from p in db.ParentTable
            join t in db.ChildTable on new {A = (int)(p.child_ID ?? default(T)), B = p.OtherID}
            equals new {A = t.ID, B = t.OtherID} into j1
            from c in j1.DefaultIfEmpty()
            select new
            {
               //...
            };

Answer 2

You can use GetValueOrDefault() method. It retrieves the value of the current Nullable object, or the object's default value.

In terms of your example :

var query = from p in db.ParentTable
            join t in db.ChildTable on new {A = p.child_ID.GetValueOrDefault(0), B = p.OtherID}
            equals new {A = t.ID, B = t.OtherID} into j1
            from c in j1.DefaultIfEmpty()
            select new
            {
                ...
            };

If the p.child_ID become null than it will return 0. Hope this will help !!