Question

I want to use LINQ-to-objects to query a collection of objects several levels deep, to extract a value. For example, given an Entity object I want to get the emailAddress string if a flag is set to 1, otherwise null:

 Entity.CommunicationCollection.Communication.CommunicationDetail.EmailAddress

Where CommunicationDetail looks like this:

 public class CommunicationDetail
 {
     public int Flag;
     public string EmailAddress;
 }

The query I came up with looks like this:

 string email = Entity.CommunicationCollection.FirstOrDefault(x => x.Communication.CommunicationDetail.Flag == 1).EmailAddress;

The problem with this is that any null objects in the hierarchy will cause a null ref exception. Is there a way to structure the query to somehow ignore the nulls, without first checking every object? (The above is a simplified example, the nesting in the project I’m working on is much deeper.)

Answer 1

Well, you either have to check everything or use ?? for defaulting, which would still be awkward. I suspect you want something like:

var email = Entity.CommunicationCollection
                  .Where(x => x.Communication != null &&
                              x.Communication.CommunicationDetail != null &&
                              x.Communication.CommunicationDetail.Flag == 1)
                  .Select(x => x.Communication.CommunicationDetail.EmailAddress)
                  .FirstOrDefault();

Note that email can still be null here…

Obviously if x.Communication can never be null, or x.Communication.CommunicationDetail can never be null, you can remove those checks – it’s not clear what can be null in your model.