How to Handle Redundant XML Namespace Declarations in Nested FOR XML PATH Queries?

Handling Repeated XML Namespace in Nested FOR XML PATH Queries

When utilizing FOR XML PATH with WITH XMLNAMESPACES to define a default namespace, unwanted namespace declarations can populate top-level nodes in nested queries that employ FOR XML.

The Issue:

Consider the following example:

;WITH XmlNamespaces( default 'uri:animal')
SELECT
    a.c2 AS "@species",
    (SELECT l.c3 AS "text()"
       FROM t2 l WHERE l.c2 = a.c1
       FOR XML PATH('leg'), TYPE) AS "legs"
FROM t1 a
FOR XML PATH('animal'), ROOT('zoo')

In this case, the namespace declaration uri:animal appears redundantly in the nested query's legs node.

Possible Solutions:

Solution 1: Using FOR XML EXPLICIT

One approach involves using FOR XML EXPLICIT in a subsequent query to remove the unwanted namespaces:

DECLARE @xml XML = (SELECT OrderID AS "@OrderID",
                        (SELECT ItemID AS "@ItemID", 
                                Name AS "data()" 
                         FROM @OrderDetail 
                         WHERE OrderID = o.OrderID 
                         FOR XML PATH ('Item'), TYPE)
                    FROM @Order o 
                    FOR XML PATH ('Order'), ROOT('dummyTag'), TYPE);

SELECT 1 AS Tag
      ,NULL AS Parent
      ,@xml AS [xml!1!!xmltext]
      ,'http://test.com/order' AS [xml!1!xmlns]
FOR XML EXPLICIT

This query uses the xml!1!!xmltext directive to extract the contents of the root node, discarding the redundant namespace.

Solution 2: Removing the XMLNS Namespace

An alternate approach involves removing the XMLNS namespace declaration from the nested query:

WITH XmlNamespaces( default 'uri:animal')
SELECT
    a.c2 AS "@species",
    (SELECT l.c3 AS "text()"
       FROM t2 l WHERE l.c2 = a.c1
       FOR XML PATH('leg'), REMOVE(NAMESPACES(), 'default'), TYPE) AS "legs"
FROM t1 a
FOR XML PATH('animal'), ROOT('zoo')

Conclusion:

The optimal solution depends on the specific requirements and complexity of the query. The FOR XML EXPLICIT method provides greater flexibility but may be more tedious for complex queries, while removing the XMLNS namespace offers a simpler approach.

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