Hi Lee!

I'm actually having this same problem. Here's the version info:

• Ditto: 0.10.0
• CorePropertyValueConverters: 3.1.1

Thanks for the help! :)

Cheers, Janae

Hi Janae,

Someone else mentioned an issue with RelatedLinks on our Gitter chat. Jeavon was on there and said that his demo site has a working example of this, with latest Ditto.

Do you have a stack trace of the error, it'd be good to see where it's falling over.

Thanks, Lee

Yep, absolutely!

Here's where I'm calling it in my model:

    /// <summary>
    /// This is the main navigation that is displayed by the logo
    /// </summary>
    public RelatedLinks MainNav { get; set; }

And here's the stack strace:

[InvalidOperationException: Sequence contains no elements]
   System.Linq.Enumerable.First(IEnumerable`1 source) +415
   Our.Umbraco.Ditto.EnumerableConverterAttribute.ProcessValue() +457
   Our.Umbraco.Ditto.DittoCacheableAttribute.GetCacheItem(DittoCacheContext cacheContext, Func`1 refresher) +121
   Our.Umbraco.Ditto.PublishedContentExtensions.DoGetProcessedValue(IPublishedContent content, CultureInfo culture, Type targetType, PropertyInfo propertyInfo, PropertyDescriptor propertyDescriptor, Type defaultProcessorType, IEnumerable`1 processorContexts) +1276
   Our.Umbraco.Ditto.PublishedContentExtensions.GetProcessedValue(IPublishedContent content, CultureInfo culture, Type targetType, PropertyInfo propertyInfo, Object instance, Type defaultProcessorType, IEnumerable`1 processorContexts) +685
   Our.Umbraco.Ditto.PublishedContentExtensions.ConvertContent(IPublishedContent content, Type type, CultureInfo culture, Object instance, IEnumerable`1 processorContexts, Action`1 onConverting, Action`1 onConverted) +2565
   Our.Umbraco.Ditto.PublishedContentExtensions.As(IPublishedContent content, Type type, CultureInfo culture, Object instance, IEnumerable`1 processorContexts, Action`1 onConverting, Action`1 onConverted) +706
   Our.Umbraco.Ditto.PublishedContentExtensions.As(IPublishedContent content, CultureInfo culture, T instance, IEnumerable`1 processorContexts, Action`1 onConverting, Action`1 onConverted) +110
   Olympic.Web.Controllers.BaseSurfaceController`1.Index(RenderModel model) +202
   lambda_method(Closure , ControllerBase , Object[] ) +94
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +229
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +35
   System.Web.Mvc.Async.AsyncControllerActionInvoker.<BeginInvokeSynchronousActionMethod>b__39(IAsyncResult asyncResult, ActionInvocation innerInvokeState) +39
   System.Web.Mvc.Async.WrappedAsyncResult`2.CallEndDelegate(IAsyncResult asyncResult) +71
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +42
   System.Web.Mvc.Async.AsyncInvocationWithFilters.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3d() +72
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +386
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +386
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +386
   System.Web.Mvc.Async.<>c__DisplayClass46.<InvokeActionMethodFilterAsynchronouslyRecursive>b__3f() +386
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +42
   System.Web.Mvc.Async.<>c__DisplayClass2b.<BeginInvokeAction>b__1c() +38
   System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +186
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +38
   System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +29
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +53
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +36
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +38
   System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +44
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +67
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +399
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +157

Thanks Janae, hmmm, so it is Ditto! I'll take a look :-)

Thanks, Lee! I will wait with baited breath ;)

OK, it is a bug (I think) in Ditto. Get ready for a long story...

We try to do some clever stuff when dealing with enumerables, specifically when we want to return an empty enumerable. This is where the exception happens when we try to figure out the type of enumerable:

https://github.com/leekelleher/umbraco-ditto/blob/develop/src/Our.Umbraco.Ditto/ComponentModel/Processors/EnumerableConverterAttribute.cs#L76

Now the object type we're dealing with is RelatedLinks (from Jeavon's Core PropertyValueConverters project), while this appears like a concrete class, it's actually inherits from an IEnumerable<RelatedLink>.

https://github.com/Jeavon/Umbraco-Core-Property-Value-Converters/blob/v3/Our.Umbraco.PropertyConverters/Models/RelatedLinks.cs

Soooo, Ditto tries to figure out what the enumerable type is.... but it can't, since it's an inherited class. Doh!

Now here's the catch... this error only occurs if the RelatedLinks value is null. So the super-super-quick fix is populate the content for that property.

For a "proper" fix, we have a couple of options... we could ignore this and return a null or figure out how to get the inherited enumerable type. (But then this raises questions about how far down the inheritance we check - eek!)

... or an alternative is for someone (somewhere) to submit a PR to Jeavon's repo to change the converter from returning a null to returning an Enumerable.Empty<RelatedLink>?

https://github.com/Jeavon/Umbraco-Core-Property-Value-Converters/blob/v3/Our.Umbraco.PropertyConverters/RelatedLinksPropertyConverter.cs

Anyway, I'll raise this on our Ditto GitHub for review.

Cheers,
- Lee

Lee,

Wow, yes, that sounds complicated! Perhaps the best option would be to do a PR... I'll look at the code you linked and see how intimidated I am by it, haha ;)

Thanks for checking into this so quickly. The navigation should never be empty, so I'll add some dummy content into it, but of course I would love to see (and help if I can!) a proper fix for the issue.

Cheers, Janae

If it's any consolation, it's code that James South wrote, so I'm equally trying to figure out the magic of it :-)

But it's a good edge-case for Ditto that we haven't been able to replicate - until now, so all good!

I think a PR on CorePropertyValueConverters is the path of least resistance.

Cheers,
- Lee

I agree! As quick note, while this doesn't fix the problem at it's root, this was a quick & dirty way for me to get around it in my project for anyone else who's wanting to use them both as well and needs a faster solution :)

/// <summary>
/// This is the main navigation that is displayed by the logo
/// </summary>
[DittoIgnore]
public RelatedLinks MainNav
{
    get { return Content.GetPropertyValue<RelatedLinks>("mainNav"); }
}

OK, you win, that's the quickest way to workaround it! :-)

Yeah, it's still an issue.

We have a failing unit-test (in a separate branch) on Ditto (PR #195), but with no current resolution (and we're not actively looking at it).

Quickest resolution is Janae's workaround... or to come up with an alternative suggestion?

Cheers,
- Lee

I've been working on a fix which passes all tests so hopefully we should have a release out very soon.

https://github.com/leekelleher/umbraco-ditto/pull/195