Test if parent objects exists

Question

I am using a lot of database data in my project that is exported in different classes. For example, I have

transaction.Layout.Multimedia.Images.first();

The problem is that these properties are not necessarily available.

So, it is possible that transaction.Layout is null, it is possible that transaction.Layout.Multimedia is null, and so on.

I currently use this for every property:

if (transaction.Layout != null)
{
    if (transaction.Layout.Multimedia != null)
    {
        if (transaction.Layout.Multimedia.Images != null)
        {
            if (transaction.Layout.Multimedia.Images.count > 0)
            {
                var img = transaction.Layout.Multimedia.Images.first();
            }
        }
    }
}

I was wondering if there is a better way that I can check all parent classes to make sure that the property I need is available. These aren't the only objects I use, there are others as well with totally different names.

Thanks in advance

Answer 1

No, there is not yet. The new version of .NET (Roslyn) has the Null propagating operator.

Then you could do:

if (transaction?.Layout?.Multimedia?.Image?.count > 0)
{
    var img = transaction.Layout.Multimedia.Images.first();
}

For now, we are stuck with this. You could minimize the rows needed by concatenating the checks, like this:

if ( transaction.Layout != null
     && transaction.Layout.Multimedia != null
     && transaction.Layout.Multimedia.Images != null
     && transaction.Layout.Multimedia.Images.count > 0
   )
{
    var img = transaction.Layout.Multimedia.Images.first();
}

There is nothing more to do.

Answer 2

You can try to use Maybe monad. More detailed description is given at Chained null checks and the Maybe monad

With and If extension methods would allow you to write:

var img = transaction.With(x => x.Layout)
                     .With(x => x.Multimedia)    
                     .With(x => x.Images)
                     .If(x => x.count > 0))
                     .With(x => x.first());

With method looks like:

public static TResult With<TInput, TResult>(this TInput o, Func<TInput, TResult> evaluator)
  where TResult : class where TInput : class
{
  if (o == null) return null;
  return evaluator(o);
}

If method:

public static TInput If<TInput>(this TInput o, Func<TInput, bool> evaluator) 
  where TInput : class
{
  if (o == null) return null;
  return evaluator(o) ? o : null;
}