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Add namespaces to queries using WITH XMLNAMESPACES

  • Artikkeli

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

WITH XMLNAMESPACES (Transact-SQL) provides namespace URI support in the following way:

Use WITH XMLNAMESPACES in FOR XML queries

WITH XMLNAMESPACES lets you include XML namespaces in FOR XML queries. For example, consider the following FOR XML query:

SELECT ProductID, Name, Color
FROM   Production.Product
WHERE  ProductID IN (316, 317)
FOR XML RAW;

This is the result:

<row ProductID="316" Name="Blade" />
<row ProductID="317" Name="LL Crankarm" Color="Black" />

To add namespaces to the XML constructed by the FOR XML query, first specify the namespace prefix to URI mappings by using the WITH NAMESPACES clause. Then, use the namespace prefixes in specifying the names in the query as shown in the following modified query. The WITH XMLNAMESPACES clause specifies the namespace prefix (ns1) to URI (uri) mapping. The ns1 prefix is then used in specifying the element and attribute names to be constructed by the FOR XML query.

WITH XMLNAMESPACES ('uri' as ns1)
SELECT ProductID as 'ns1:ProductID',
       Name      as 'ns1:Name',
       Color     as 'ns1:Color'
FROM  Production.Product
WHERE ProductID IN (316, 317)
FOR XML RAW ('ns1:Prod'), ELEMENTS;

The XML result includes the namespace prefixes:

<ns1:Prod xmlns:ns1="uri">
  <ns1:ProductID>316</ns1:ProductID>
  <ns1:Name>Blade</ns1:Name>
</ns1:Prod>
<ns1:Prod xmlns:ns1="uri">
  <ns1:ProductID>317</ns1:ProductID>
  <ns1:Name>LL Crankarm</ns1:Name>
  <ns1:Color>Black</ns1:Color>
</ns1:Prod>

The following applies to the WITH XMLNAMESPACES clause:

  • It is supported only on the RAW, AUTO, and PATH modes of the FOR XML queries. The EXPLICIT mode isn't supported.

  • It only affects the namespace prefixes of FOR XML queries and the xml data type methods, but not the XML parser. For example, the following query returns an error, because the XML document has no namespace declaration for the myNS prefix.

  • The FOR XML directives, XMLSCHEMA and XMLDATA can't be used when a WITH XMLNAMESPACES clause is being used.

    CREATE TABLE T (x xml);
GO
WITH XMLNAMESPACES ('https://abc' as myNS )
INSERT INTO T VALUES('<myNS:root/>');
GO

Use the XSINIL directive

You can't define the xsi prefix in the WITH XMLNAMESPACES clause if you're using the ELEMENTS XSINIL directive. Instead, it's added automatically when you use ELEMENTS XSINIL. The following query uses ELEMENTS XSINIL that generates element-centric XML where null values are mapped to elements that have the xsi:nil attribute set to True.

WITH XMLNAMESPACES ('uri' as ns1)
SELECT ProductID as 'ns1:ProductID',
       Name      as 'ns1:Name',
       Color     as 'ns1:Color'
FROM Production.Product
WHERE ProductID = 316
FOR XML RAW, ELEMENTS XSINIL;

This is the result:

<row xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:ns1="uri">
  <ns1:ProductID>316</ns1:ProductID>
  <ns1:Name>Blade</ns1:Name>
  <ns1:Color xsi:nil="true" />
</row>

Specify default namespaces

Instead of declaring a namespace prefix, you can declare a default namespace by using a DEFAULT keyword. In the FOR XML query, it will bind the default namespace to XML nodes in the resulting XML. In the following example, the WITH XMLNAMESPACES defines two namespace prefixes that are defined together with a default namespace.

WITH XMLNAMESPACES ('uri1' as ns1,
                    'uri2' as ns2,
                    DEFAULT 'uri2')
SELECT ProductID,
      Name,
      Color
FROM Production.Product
WHERE ProductID IN (316, 317)
FOR XML RAW ('ns1:Product'), ROOT('ns2:root'), ELEMENTS;

The FOR XML query generates element-centric XML. The query uses both the namespace prefixes in naming nodes. In the SELECT clause, the ProductID, Name, and Color don't specify a name with any prefix. Therefore, the corresponding elements in the resulting XML belong to the default namespace.

<ns2:root xmlns="uri2" xmlns:ns2="uri2" xmlns:ns1="uri1">
  <ns1:Product>
    <ProductID>316</ProductID>
    <Name>Blade</Name>
  </ns1:Product>
  <ns1:Product>
    <ProductID>317</ProductID>
    <Name>LL Crankarm</Name>
    <Color>Black</Color>
  </ns1:Product>
</ns2:root>

The following query is similar to the previous one, except that the FOR XML AUTO mode is specified.

WITH XMLNAMESPACES ('uri1' as ns1,  'uri2' as ns2,DEFAULT 'uri2')
SELECT ProductID,
      Name,
      Color
FROM Production.Product as "ns1:Product"
WHERE ProductID IN (316, 317)
FOR XML AUTO, ROOT('ns2:root'), ELEMENTS;

Using predefined namespaces

When you use predefined namespaces, except the xml namespace and the xsi namespace when ELEMENTS XSINIL is used, you must explicitly specify the namespace binding by using WITH XMLNAMESPACES. The following query explicitly defines the namespace prefix to URI binding for the predefined namespace (urn:schemas-microsoft-com:xml-sql).

WITH XMLNAMESPACES ('urn:schemas-microsoft-com:xml-sql' as sql)
SELECT 'SELECT * FROM Customers FOR XML AUTO, ROOT("a")' AS "sql:query"
FOR XML PATH('sql:root');

This is the result. SQLXML users are familiar with this XML template. For more information, see SQLXML 4.0 Programming Concepts.

<sql:root xmlns:sql="urn:schemas-microsoft-com:xml-sql">
  <sql:query>SELECT * FROM Customers FOR XML AUTO, ROOT("a")</sql:query>
</sql:root>

Only the xml namespace prefix can be used without explicitly defining it in WITH XMLNAMESPACES, as shown in the following PATH mode query. Also, if the prefix is declared, it has to be bound to the namespace http://www.w3.org/XML/1998/namespace. The names specified in the SELECT clause refer to the xml namespace prefix that isn't explicitly defined by using WITH XMLNAMESPACES.

SELECT 'en'    as "English/@xml:lang",
       'food'  as "English",
       'ger'   as "German/@xml:lang",
       'Essen' as "German"
FOR XML PATH ('Translation');
GO

The @xml:lang attributes use the predefined xml namespace. Because XML version 1.0 doesn't require the explicit declaration of the xml namespace binding, the result won't include an explicit declaration of the namespace binding.

This is the result:

<Translation>
  <English xml:lang="en">food</English>
  <German xml:lang="ger">Essen</German>
</Translation>

Use WITH XMLNAMESPACES with the xml data type methods

The xml Data Type Methods specified in a SELECT query, or in UPDATE when it's the modify() method, all have to repeat the namespace declaration in their prolog. This can be time-consuming. For example, the following query retrieves product model IDs whose catalog descriptions do include specification. That is, the <Specifications> element exists.

SELECT ProductModelID, CatalogDescription.query('
declare namespace pd="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
    <Product
        ProductModelID= "{ sql:column("ProductModelID") }"
        />
') AS Result
FROM Production.ProductModel
WHERE CatalogDescription.exist('
    declare namespace  pd="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";
     /pd:ProductDescription[(pd:Specifications)]'
    ) = 1;

In the previous query, both the query() and exist() methods declare the same namespace in their prolog. For example:

declare namespace pd="https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription";

Alternatively, you can declare WITH XMLNAMESPACES first and use the namespace prefixes in the query. In this case, the query() and exist() methods don't have to include namespace declarations in their prolog.

WITH XMLNAMESPACES ('https://schemas.microsoft.com/sqlserver/2004/07/adventure-works/ProductModelDescription' as pd)
SELECT ProductModelID, CatalogDescription.query('
    <Product
        ProductModelID= "{ sql:column("ProductModelID") }"
        />
') AS Result
FROM Production.ProductModel
WHERE CatalogDescription.exist('
     /pd:ProductDescription[(pd:Specifications)]'
    ) = 1;
GO

An explicit declaration in the XQuery prolog overrides the namespace prefix and the default element namespace that are defined in the WITH clause.

See also