Using RdfProperty of array to custom class

Question

I have defined:

[RdfSerializable]
public class SomeItem
{
   // Unique identificator of the resource
   [ResourceUri]
   public string ID { get; set; }

   [RdfProperty( true )]
   public string SomeData { get; set; }
}

and in some other class: 

[RdfProperty(true)]
public SomeItem[] MyTestProp
{
   get
   {
      return new SomeItem[] { new SomeItem() { ID="1", SomeData="test1" }, new SomeItem() { ID="2", SomeData = "test2" } };
   }
}

When I try to serialize the class that contains this custom "MyTestProp" and it gave me that message:

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Am I wrong in defining those properties or there is a special way to define array to custom class? Note that serializing array to string for example is not crashing me that way, but it is working.

Whole source:

using System;
using NC3A.SI.Rowlex;

[assembly: Ontology("ROWLEXtest1", "http://www.test.com/MyOntology")]

namespace ROWLEXtest1
{
   [RdfSerializable( HasResourceUri=false )]
   public class Item
   {
      [RdfProperty(true)]
      public string MyProp;
   }

   [RdfSerializable]
   public class AllItems
   {
      [RdfProperty(true)] public string mTitle;

      private int id = new Random().Next(0, 20);

      [ResourceUri]
      public string ResourceUri 
      {
         get { return "This " + id.ToString(); }
      }

      [RdfProperty(false)]
      public Item[] Items;
   }

   class Program
   {
      static void Main(string[] args)
      {
         var item = new AllItems();
         item.mTitle = "Hello World!";
         item.Items = new Item[] { new Item(){ MyProp = "test1" }, new Item(){ MyProp = "test2" } };

         var doc = Rdfizer.Serialize(item);

         System.Console.Out.Write(doc.ToString());
      }
   }
}

Exception is:

System.NullReferenceException was unhandled Message="Object reference not set to an instance of an object." Source="NC3A.SI.Rowlex" StackTrace: at NC3A.SI.Rowlex.RdfPropertyAttribute.ExtractRange(MemberInfo memberInfo, Int32& minCardinality, Int32& maxCardinality) at NC3A.SI.Rowlex.RdfPropertyAttribute.ExtractRange(MemberInfo memberInfo) at NC3A.SI.Rowlex.Rdfizer.AppendProperty(RdfDocument doc, MemberInfo memberInfo, RdfPropertyAttribute attribute, Object item, String resourceUri) at NC3A.SI.Rowlex.Rdfizer.AppendSingleRdfSerializableObject(RdfDocument doc, Object item) at NC3A.SI.Rowlex.Rdfizer.ProcessItem(RdfDocument doc, Object item, String[] rangeTypeUris) at NC3A.SI.Rowlex.Rdfizer.ExecuteSerialization(IEnumerable objects) at NC3A.SI.Rowlex.Rdfizer.Serialize(IEnumerable objects, Boolean tolerateUnserializebleObjects) at NC3A.SI.Rowlex.Rdfizer.Serialize(Object item) at ROWLEXtest1.Program.Main(String[] args) in C:\ROWLEXtest1\ROWLEXtest1\Program.cs:line 40 at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args) at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly() at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state) at System.Threading.ThreadHelper.ThreadStart() InnerException:

Answer 1

What you did looks OK but there is one error: RdfProperty declaration should take "false" for MyTestProp as MyTestProp is not a data type property but object property (it returns objects and not literals).

However, I am not sure that this is the root of your problem. And even if it is, you should get a decent error message with meaningful text instead of silly NullReferenceException. Therefore, I would like to try to reproduce your error and provide a fix if applicable. Could you please, specify

• the class and its decoration that hosts the MyTestProp,
• the code where you instantiate that class, and
• the code you use to for serialization.
• Had you apply assembly level attributes (for ontology - namespace mapping), please indicate that, too.

Maybe you could consider sending me your code sample to [admin at rowlex.net].

EDIT: I could reproduce the exception, it is a bug in ROWLEX. The fixed 2.0.1 version can now downloaded from the ROWLEX site.