Not all PVCs return a correct XPath value

In Umbraco 7 I’m using the following XPath query to fetch the ‘Not found’ error page: //error[statusCode='404'], where the statusCode property is selected from a dropdown (Umbraco.DropDown.Flexible, enable multiple choice disabled and prevalues: 404 and 500).

This XPath query doesn’t work anymore in Umbraco 8, although //error does (so it’s something with the statusCode='505' part). After checking the source of FlexibleDropdownPropertyValueConverter, it always returns System.String[] (the literal string value) as XPath value, because the intermediate value is a string[]:

https://github.com/umbraco/Umbraco-CMS/blob/3bfd9b71e290354744d677440983ecd06c5c0788/src/Umbraco.Web/PropertyEditors/ValueConverters/FlexibleDropdownPropertyValueConverter.cs#L19-L25

And the XPath value is returned from PropertyValueConverterBase by just doing a ToString() on it: https://github.com/umbraco/Umbraco-CMS/blob/3bfd9b71e290354744d677440983ecd06c5c0788/src/Umbraco.Core/PropertyEditors/PropertyValueConverterBase.cs#L45-L46

Looking at some other Property Value Converters, these all seem to return wrong XPath values:

• FlexibleDropdownPropertyValueConverter returns System.String[] instead of the comma seperated values
• MediaPickerValueConverter returns Umbraco.Core.Udi[] instead of the comma seperated UDI values
• MultiNodeTreePickerValueConverter returns Umbraco.Core.Udi[] instead of the comma seperated UDI values

Reproduction

Bug summary

UmbracoContext.Cache.GetByXPath("//error[statusCode='404']") does not return content, because the XPath value from the FlexibleDropdownPropertyValueConverter isn’t 404, but System.String[].

Specifics

Latest version: Umbraco 8.1.5

Steps to reproduce

• Create a document type with alias error
• Add a property statusCode using Umbraco.DropDown.Flexible, enable multiple choice disabled and prevalue: 404
• Add content using the document type, select 404 in the dropdown, publish
• Try to query by XPath: //error[statusCode='404']

Expected result

Return the content matched by the XPath query.

Actual result

Nothing returned, as the statusCode value doesn’t match.

[zpqrtbnk]

Methods:

• IPropertyValueConverter.ConvertIntermediateToXPath(...) converts the “intermediate” value into an XPath value (a string or an Xml fragment, more on this later) - this is where the actual work happens.
• IPublishedPropertyType.ConvertInterToXPath(...) uses the above method from the converter for that type to convert the “intermediate” value into the XPath value, and manages the caching of the result.
• IPublishedProperty.GetXPathValue(...) returns the XPath value (a string or an Xml fragment) of a property - which is obtained via the above methods.

Which means that the only thing you need to bother implementing is the first one, the rest is plumbing that you should not need to bother about.

The method can return either a string, which will then be the property value in the Xml view of the cache, eg <firstName>John</firstName>. But it can also return an Xml fragment, as an XPathNavigator. The MultipleTextStringValueConverter in Core implements such a conversion, and returns something that, in the Xml view of the cache, will look like

<firstNames>
    <value>John</value>
    <value>Barbara</value>
</firstNames>

[zpqrtbnk]

Yup, valid comment about returning values or not - and then, only the elements. Glad it works!