Supply xml element value in modify() method - sql-server

Question

I know how to replace element value for the xml element in the modify() method. Here's the example
TSQL Replace value in XML String
My problem is a bit different. Taking example from above link...
UPDATE dbo.TFS_Feedback_New
SET Details.modify('
replace value of (/optional/educational/text())[1]
with sql:variable("#updatedEducation")')
WHERE feedbackID = #FBID
What I want to do is provide value for 'educational'. In other words I want to do something like this
UPDATE dbo.TFS_Feedback_New
SET Details.modify('
replace value of (/optional/sql:variable("#name")/text())[1]
with sql:variable("#value")')
WHERE feedbackID = #FBID
I'm getting the following error because of sql:variable("#name")
The XQuery syntax '/function()' is not supported.
How can I pass both the name of the element to be updated and its value to my
stored procedure and have it update the XML column?

Answer 1

You are not allowed to use variables as part of the XPath, but you can use a predicate:
DECLARE #xml XML=
N'<root>
<optional>
<educational>SomeText</educational>
<someOther>blah</someOther>
</optional>
</root>';
--The straight approach as you know it:
SET #xml.modify('replace value of (/root/optional/educational/text())[1] with "yeah!"');
SELECT #xml;
--Now we use a variable to find the first node below <optional>, which name is as given:
DECLARE #ElementName VARCHAR(100)='educational';
SET #xml.modify('replace value of (/root/optional/*[local-name()=sql:variable("#ElementName")]/text())[1] with "yeah again!"');
SELECT #xml;
Try it out...