Question

If a AJAX-Enabled WCF should return an Object with a Date Property which is Nothing a Request to this Service fails.

Test.svc

Imports System.ServiceModel
Imports System.ServiceModel.Activation
Imports System.ServiceModel.Web
Imports System.Runtime.Serialization

<ServiceContract(Namespace:="WebApp")>
<AspNetCompatibilityRequirements(RequirementsMode:=AspNetCompatibilityRequirementsMode.Allowed)>
Public Class Test

   <OperationContract()>
   <WebGet()>
   Public Function TestOperation() As CompositeType
      Dim obj As New CompositeType
      obj.DateProp = Nothing
      obj.StringProp = "Test"
      Return obj
   End Function

End Class

<DataContract()>
Public Class CompositeType
   <DataMember()>
   Public Property DateProp() As Date
   <DataMember()>
   Public Property StringProp() As String

End Class

scripttag on Testform.aspx

<script type="text/javascript">
   $(document).ready(function () {
      $.getJSON('./Test.svc/TestOperation', function (data) {
         alert(data.d.DateProp);
      });
   });
</script>

Web.config (serviceModel section)

<system.serviceModel>
    <behaviors>
        <endpointBehaviors>
            <behavior name="WebApp.TestAspNetAjaxBehavior">
                <enableWebScript />
            </behavior>
        </endpointBehaviors>
    </behaviors>
    <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
    <services>   
        <service name="WebApp.Test">
        <endpoint address="" behaviorConfiguration="WebApp.TestAspNetAjaxBehavior"
        binding="webHttpBinding" contract="WebApp.Test" />
        </service>
    </services>
</system.serviceModel>

Chrome displays on this call the following error message: “failed to load resource”.

Has anyone an explanation/idea for this behaviour and how are you supposed to prevent this problem?

Thanks for your advice 😉

Answer 1

If you want to be able to assign Nothing to a DateTime field you should make it nullable:

<DataMember()>
Public Property DateProp() As Nullable(Of DateTime)

I am not a VB.NET expert but as far as I know the Date keyword in VB.NET is an alias to the DateTime structure (which is not nullable), except that VB.NET must be doing some black voodoo magic to allow you to assign Nothing to it. Except that when the serializer attempts to serialize it into JSON the following exception is thrown:

There was an error while trying to serialize parameter
WebApp:TestOperationResult. The InnerException message was ‘DateTime
values that are greater than DateTime.MaxValue or smaller than
DateTime.MinValue when converted to UTC cannot be serialized to
JSON.’. Please see InnerException for more details.