Question

I have the following LINQ query:

DataClassesDataContext dc = new DataClassesDataContext();  var query = from contact in dc.Contacts             select new             {                 ContactId = contact.ContactId,                 LastName = contact.LastName,                 FirstName = contact.FirstName,                 Addresses = contact.Addresses,                 Phones = contact.Phones,                 DOB = contact.BirthDate,                 LastNote = contact.Notes.Max(n => n.Created), //this line causes the error                 Status = contact.ContactStatus.ContactStatusName,                 EmailAddress = contact.Emails             }; 

The line where I get the maximum created date for the notes collection causes the following exception to be thrown:

Exception: The null value cannot be assigned to a member with type System.DateTime which is a non-nullable value type.

How do I write the query to allow null values into the LastNote field? The DOB field is defined as DateTime? and has not problem handling nulls.

Answer 1

Think I figured it out.

If I cast the maximum note value to a nullable DateTime it seems to eliminate the exception. The following change worked for me:

LastNote = (Nullable<DateTime>)contact.Notes.Max(n => n.Created) 

As others have pointed out, it can also be written using the shorthand notation for a nullable DateTime as follows:

LastNote = (DateTime?) contact.Notes.Max(n => n.Created)