The key difference (*boom tish*) is that the one that is apparently broken will get the value from the umbraco.config file. If you recently did an upgrade, I could see that file having not been updated to add keys to each XML element. In particular, each XML element that represents a page in that file should look something like this:

<someDoctype id="1111" key="11111111-1111-1111-1111-111111111111" parentID="-1" level="1" creatorID="1" sortOrder="0" createDate="2011-01-11T11:11:11" updateDate="2011-01-11T11:11:11" nodeName="Some Node Name" urlName="whatevs" path="-1,1111" isDoc="" nodeType="2222" creatorName="someUser" writerName="someUser" writerID="1" template="0" nodeTypeAlias="someDoctype">

Note the key attribute after the id attribute. If you don't see that, try deleting the file and recycling your app pool so that it gets regenerated.

Hi Nicholas

Thank you for response, I checked umbraco.config and key attribute is filled with right Guid, but "IPublishedContent.GetKey()" doesn't work.

Hi Nik

Model.Content.GetKey() returns emty Guid too.

Thanks, Nik!

I think this needs to be a simplified. Anyway, thanks to Nik and and Nicholas I created an extension method to make sure this would work from modelsbuilder objects as well as other content:

public static Guid GetGuid(this IPublishedContent content)
{
    var contentWithKey = content as IPublishedContentWithKey;
    if (contentWithKey != null)
        return contentWithKey.Key;
    if (content is PublishedContentWrapped)
    {
        contentWithKey = ((PublishedContentWrapped)content).Unwrap() as IPublishedContentWithKey;
        if (contentWithKey != null)
            return contentWithKey.Key;
    }
    return Guid.Empty;
}

I created the following extension methods to make working with GUIDs and UDIs much less painful and reliable. Hope they help someone!

The following extension method should return a IPublishedContentWithKey from IPublishedContent:

/// <summary>
/// Gets the published content with a guaranteed key
/// </summary>
/// <param name="content">The published content</param>
/// <returns>A published content with key</returns>
/// <remarks>
/// Workaround for the fact that GetKey() doesn't always work - see http://issues.umbraco.org/issue/U4-10128
/// </remarks>
public static IPublishedContentWithKey GetContentWithKey(this IPublishedContent content)
{
    var withKey = content as IPublishedContentWithKey;

    if (withKey != null)
        return withKey;

    var wrapped = content as PublishedContentWrapped;

    if (wrapped != null)
        return GetContentWithKey(wrapped.Unwrap());

    return null;
}

The following method should guarantee to return a GUID key from IPublishedContent:

/// <summary>
/// Guaranteed to return a GUID
/// </summary>
/// <param name="content">The published content</param>
/// <returns>A Guid</returns>
public static Guid GetKeyGuaranteed(this IPublishedContent content)
{
    var contentWithKey = content.GetContentWithKey();
    return contentWithKey != null ? contentWithKey.GetKey() : Guid.Empty;
}

The following extension method should return a UDI from IPublishedContent:

/// <summary>
/// Gets an Umbraco UDI
/// </summary>
/// <param name="content">The published content</param>
/// <param name="objectType">The type of UDI to create</param>
/// <returns>An Umbraco Document Identifier</returns>
public static Udi GetUdi(this IPublishedContent content, UmbracoObjectTypes objectType)
{
    string type = Constants.UdiEntityType.FromUmbracoObjectType(objectType);
    return Udi.Create(type, content.GetKeyGuaranteed());
}

You'll need to include the Umbraco.Core namespace.

Hi Edgar. The GetContentWithKey is an extension method I created. So you will first need to create a static class and add the methods shown in my post to it. Then you will need to reference it via the namespace you chose for the class. ie. if you put it in the MyProject.Extensions namespace you'd need to add @using MyProject.Extensions in your view.

See https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members or https://www.c-sharpcorner.com/UploadFile/74ce7b/static-class-in-C-Sharp/ if you are not familiar with static classes.

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