How to cast varchar to XML in an OUTER APPLY query

Question

Given the following sample SQL, it would work perfectly IF the two varchar(max) declarations for both the XML itself and the @t table declaration were actually xml field types.

DECLARE @x varchar(max) = '<?xml version="1.0" encoding="UTF-8"?>
<AuditTrail>
   <Action />
   <ActionDetail />
   <ChangesXML>
      <Details>
         <Object ObjectType="Data.Review_Extension" AuditType="Modified" FriendlyName="Review">
            <ObjectKeys>
               <ReviewExtID>21482283</ReviewExtID>
            </ObjectKeys>
            <Properties>
               <Property name="Document Type 01" FieldName="Document_Type_01" TemplateFieldID="644140" ReviewExtensionID="214822182" PropertyType="System.String">
                  <OldValue />
                  <NewValue><![CDATA[1145]]></NewValue>
               </Property>
               <Property name="Document Type 02" FieldName="Document_Type_02" TemplateFieldID="644141" ReviewExtensionID="21482283" PropertyType="System.String">
                  <OldValue />
                  <NewValue><![CDATA[123]]></NewValue>
               </Property>
            </Properties>
         </Object>
      </Details>
   </ChangesXML>
</AuditTrail>'

DECLARE @t TABLE (userid INT, [xml] varchar(max))
INSERT @t VALUES(1, @x)

SELECT t.userid, r.z.value('@FieldName', 'nvarchar(MAX)')
FROM @t t
OUTER APPLY t.xml.nodes('//Property') as r(z) 

How can I modify the SELECT query at the bottom of this SQL to cast the [xml] field to an XML field type so that I can use t.xml.nodes?

Answer 1

Just use one OUTER APPLY first to force a CAST :

SELECT t.userid, r.z.value('@FieldName', 'nvarchar(MAX)')
FROM @t t
OUTER APPLY (SELECT CAST(t.xml as xml) as realxml) s
OUTER APPLY s.realxml.nodes('//Property') as r(z)