How to update XML attributes based on existing values in SQL? - sql-server

Question

I have a lot of XML documents in the app which are stored in the SQL Server database. Here is an example:
<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Blue">test</emphasis>
<emphasis color="Red">test</emphasis>
</emphasis>
<emphasis>
<emphasis color="Green">test</emphasis>
</emphasis>
</para>
I want to replace the values of color attributes for all emphasis and entry elements with the corresponding Hex color code. This is what i want to get:
<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="0000FF">test</emphasis>
<emphasis color="FF0000">test</emphasis>
</emphasis>
<emphasis>
<emphasis color="008000">test</emphasis>
</emphasis>
</para>
So i will need some kind of switch/case. Note: attribute could have any hex value (not just red, green, blue):
DECLARE #ColorTextValue VARCHAR(20) = 'Blue'
DECLARE #ColorHexValue VARCHAR(6)
SET #ColorHexValue = CASE #ColorTextValue
WHEN 'Blue' THEN '0000FF'
WHEN 'Red' THEN 'FF0000'
WHEN 'Green' THEN '008000'
END
I have the following script right now:
DECLARE #tbl TABLE (XmlData XML);
INSERT INTO #tbl VALUES
('<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Blue">test</emphasis>
<emphasis color="Red">test</emphasis>
</emphasis>
<emphasis>
<emphasis color="Green">test</emphasis>
</emphasis>
</para>'
);
UPDATE
[XmlDocument]
SET
[XmlData].modify('replace value of (//*[self::emphasis or self::entry]/#color)[1] with "hexCodeHere"')
FROM
#tbl AS [XmlDocument]
WHERE
[XmlDocument].[XmlData].exist('//*[self::emphasis or self::entry][#color]') = 1
SELECT * FROM #tbl
As you can see it just has a hardcoded HexCode. How to add some kind of switch into this statement to calculate Hex code dynamically?
Also it doesn't have a possibility to update ALL attributes. It updates only the first item

Answer 1

Please try the following solution.
It creates a computed column ColorHexValue inside the CTE.
Next step is to update the XML column color attribute with the ColorHexValue column value.
SQL
-- DDL and sample data population, start
DECLARE #tbl TABLE (ID INT IDENTITY PRIMARY KEY, xmldata XML);
INSERT INTO #tbl (xmldata) VALUES
(N'<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Blue">test</emphasis>
</emphasis>
</para>'),
(N'<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Green">test</emphasis>
</emphasis>
</para>');
-- DDL and sample data population, end
-- just to see
SELECT *
FROM #tbl
CROSS APPLY (SELECT CASE xmldata.value('(/para/emphasis/emphasis/#color)[1]', 'VARCHAR(10)')
WHEN 'Blue' THEN '0000ff'
WHEN 'Red' THEN 'ff0000'
WHEN 'Green' THEN '008000'
END) t(ColorHexValue);
-- real deal
;WITH rs AS
(
SELECT *
FROM #tbl
CROSS APPLY (SELECT CASE xmldata.value('(/para/emphasis/emphasis/#color)[1]', 'VARCHAR(10)')
WHEN 'Blue' THEN '0000ff'
WHEN 'Red' THEN 'ff0000'
WHEN 'Green' THEN '008000'
END) t(ColorHexValue)
)
UPDATE rs
SET xmldata.modify('replace value of (/para/emphasis/emphasis/#color)[1] with sql:column("ColorHexValue")');
-- test
SELECT * FROM #tbl;
SQL #2
-- DDL and sample data population, start
DECLARE #tbl TABLE (ID INT IDENTITY PRIMARY KEY, xmldata XML);
INSERT INTO #tbl (xmldata) VALUES
(N'<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Blue">test</emphasis>
<emphasis color="Red">test</emphasis>
</emphasis>
<emphasis>
<emphasis color="Green">test</emphasis>
</emphasis>
</para>'),
(N'<para id="19" revDate="2022-05-04T04:00:00Z">
<emphasis>
<emphasis color="Green">test</emphasis>
</emphasis>
</para>');
-- DDL and sample data population, end
-- before
SELECT * FROM #tbl
WHERE xmldata.exist('//emphasis/#color[. = ("Blue","Red","Green")]') = 1;
DECLARE #tries INT = 0;
WHILE ##ROWCOUNT > 0 AND #tries < 100
BEGIN
UPDATE #tbl
SET xmldata.modify('replace value of (/para/emphasis/emphasis/#color[. = ("Blue","Red","Green")])[1]
with (
let $c := (/para/emphasis/emphasis/#color[. = ("Blue","Red","Green")])[1]
return
if ($c = "Blue") then "0000ff"
else if ($c = "Red") then "ff0000"
else if ($c = "Green") then "008000"
else ("unknown color")
)')
WHERE xmldata.exist('/para/emphasis/emphasis/#color[. = ("Blue","Red","Green")]') = 1;
SET #tries += 1;
END;
-- after
SELECT * FROM #tbl;
db<>fiddle