在TSQL中使用变量节点名称构造xml

Question

In my application I am running a rather complex query using FOR XML PATH() to construct an xml result. I am using this query in several stored procedures but each the root node and the first level node names are different. What I would like to do is create a scalar user defined function that takes the two node names as parameters and returns the correct xml. The expected output would look like this:

<{root node name}>
    <{first level node name}  attr1="value1" attr2="value2">
        <detail attr1="value3">
            <error code="1" descr="some error"/>
            <error code="3" descr="some other error"/>
        </detail>
    </{first level node name}>
    <error code="4" descr="yet another error"/>
</{root node name}>

With {root node name} and {first level node name} being passed as parameters

I know I can use dynamic SQL to do this but it can be very cumbersome and I would like to avoid it. I could also do it easily in C# or using XSLT but I need to do this entirely in SQL as it will be called from SQL Service broker handlers.

Unfortunately FOR XML PATH requires a literal for the node name. I also tried creating the xml with known generic node names and then trying to replace them using XQuery, but that also requires literals. Both the XQuery has to be a literal and the node names used in node constructors need to be literals as well (cannot use sql:variable() )

Is there any way create XML with dynamic node names?

Answer 1

As the elements names are built out of the result set's column names this cannot work (other than dynamic SQL or CLR), but there is rescue:

DECLARE @rowName NVARCHAR(10)=N'TheRow';
DECLARE @rootName NVARCHAR(10)=N'TheRoot';

DECLARE @OutputXml XML=
CAST(
    REPLACE(REPLACE(
    CAST((SELECT TOP 2 [name],[type] 
          FROM sys.objects 
          FOR XML PATH(N'ThisIsAStringOnlyUsedAsRowElementName')
                 ,ROOT(N'TheSameIdeaForTheRootName')
                 ,TYPE) AS NVARCHAR(MAX))
    ,N'ThisIsAStringOnlyUsedAsRowElementName',@rowName)
    ,N'TheSameIdeaForTheRootName',@rootName) AS XML);


SELECT @outputXML;

The result

<TheRoot>
  <TheRow>
    <name>spt_fallback_db</name>
    <type>U </type>
  </TheRow>
  <TheRow>
    <name>spt_fallback_dev</name>
    <type>U </type>
  </TheRow>
</TheRoot>

In general I'd avoid string manipulations on an XML (due to possible side effects and performance impact). But I think this is a legit workaround...