Error: The target of 'replace value of' must be a non-metadata attribute or an element with simple typed content

I have the following xml field in which I need to replace the value of one of the nodes:

<DataFormItem xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="bb_appfx_dataforms">
  <Values>
    <fv ID="FUNDRAISERID">
      <Value xmlns:q1="http://microsoft.com/wsdl/types/" xsi:type="q1:guid">1009fb5a-41a0-40c1-8685-d5973fb71df7</Value>
      <ValueTranslation>John Smith</ValueTranslation>
    </fv>
    <fv ID="STARTDATE">
      <Value xsi:type="xsd:dateTime">2015-01-01T00:00:00</Value>
    </fv>
  </Values>
</DataFormItem>

I need to change the STARTDATE value '2015-01-01T00:00:00' to '2016-01-01T00:00:00'. To accomplish this, I have written the following query:

update KPIINSTANCE
SET     NAME = '2016 ' + SUBSTRING(k.name, 6,150), 
        PARAMETERSXML.modify('
        declare namespace df = "bb_appfx_dataforms";
        replace value of (/df:DataFormItem/df:Values/df:STARTDATE/df:Value)[1] with "2016-01-01T00:00:00" cast as xs:dateTime ?')
FROM KPIINSTANCE K
        JOIN KPICATALOG KP ON KP.ID = K.KPICATALOGID
where k.ID = '43C6DA6B-420A-4D4E-BA31-84C8054B4AB6'

As far as I can tell, this is correct, but when I try to run the query, I get the error: XQuery [KPIINSTANCE.PARAMETERSXML.modify()]: The target of 'replace value of' must be a non-metadata attribute or an element with simple typed content, found 'element(df{bb_appfx_dataforms}:Value,xdt:untyped) ?'

Since this node is typed, I'm unsure why the error is saying it is not typed. Anyone have any ideas?

Solution

Your XPath is wrong... STARTDATE is not a node's name but it's an attribut's name below "fv"

I think this is much simpler to solve: The nodes in question don't even have a namespace prefix. Try it like this:

PARAMETERSXML.modify('replace value of (/DataFormItem/Values/fv[@ID="STARTDATE"]/Value/text())[1] with "2016-01-01T00:00:00"')

I tested like this:

DECLARE @KPIINSTANCE TABLE(ID UNIQUEIDENTIFIER, NAME VARCHAR(100),PARAMETERSXML XML);
INSERT INTO @KPIINSTANCE VALUES
('43C6DA6B-420A-4D4E-BA31-84C8054B4AB6'
,'test'
,'<DataFormItem xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="bb_appfx_dataforms">
  <Values>
    <fv ID="FUNDRAISERID">
      <Value xmlns:q1="http://microsoft.com/wsdl/types/" xsi:type="q1:guid">1009fb5a-41a0-40c1-8685-d5973fb71df7</Value>
      <ValueTranslation>John Smith</ValueTranslation>
    </fv>
    <fv ID="STARTDATE">
      <Value xsi:type="xsd:dateTime">2015-01-01T00:00:00</Value>
    </fv>
  </Values>
</DataFormItem>'
);

SELECT * FROM @KPIINSTANCE;


UPDATE @KPIINSTANCE
SET     NAME = '2016 ' + 'test', 
        PARAMETERSXML.modify('replace value of (/DataFormItem/Values/fv[@ID="STARTDATE"]/Value/text())[1] with "2016-01-01T00:00:00"')
FROM @KPIINSTANCE K
        --JOIN KPICATALOG KP ON KP.ID = K.KPICATALOGID
WHERE K.ID = '43C6DA6B-420A-4D4E-BA31-84C8054B4AB6'

SELECT * FROM @KPIINSTANCE;