expanded-QName (XQuery)

This example illustrates how you can modify the value of an element node of QName type. The example performs the following:

• Creates an XML schema collection that defines an element of QName type.

• Creates a table with an xml type column by using the XML schema collection.

• Saves an XML instance in the table.

• Uses the modify() method of the xml data type to modify the value of the QName type element in the instance. The expanded-QName() function is used to generate the new QName type value.

-- If XML schema collection (if exists)
-- drop xml schema collection SC
-- go
-- Create XML schema collection
CREATE XML SCHEMA COLLECTION SC AS N'
<schema xmlns="http://www.w3.org/2001/XMLSchema"
    xmlns:xs="http://www.w3.org/2001/XMLSchema" 
    targetNamespace="QNameXSD" 
      xmlns:xqo="QNameXSD" elementFormDefault="qualified">
      <element name="Root" type="xqo:rootType" />
      <complexType name="rootType">
            <sequence minOccurs="1" maxOccurs="1">
                        <element name="ElemQN" type="xs:QName" />
            </sequence>
      </complexType>
</schema>'
go
-- Create table.
CREATE TABLE T( XmlCol xml(SC) )
-- Insert sample XML instnace
INSERT INTO T VALUES ('
<Root xmlns="QNameXSD" xmlns:ns="http://myURI">
      <ElemQN>ns:someName</ElemQN>
</Root>')
go
-- Verify the insertion
SELECT * from T
go
-- Result
<Root xmlns="QNameXSD" xmlns:ns="http://myURI">
  <ElemQN>ns:someName</ElemQN>
</Root> 

In the following query, the <ElemQN> element value is replaced by using the modify() method of the xml data type and the replace value of XML DML, as shown.

-- the value.
UPDATE T 
SET XmlCol.modify('
  declare default element namespace "QNameXSD"; 
  replace value of /Root[1]/ElemQN 
  with expanded-QName("http://myURI", "myLocalName") ')
go
-- Verify the result
SELECT * from T
go

This is the result. Note that the element <ElemQN> of QName type now has a new value:

<Root xmlns="QNameXSD" xmlns:ns="urn">
  <ElemQN xmlns:p1="http://myURI">p1:myLocalName</ElemQN>
</Root>

The following statements remove the objects used in the example.

-- Cleanup
DROP TABLE T
go
drop xml schema collection SC
go

The expanded-QName function cannot be used in XML construction. The following example illustrates this. To work around this limitation, the example first inserts a node and then modifies the node.

-- if exists drop the table T
--drop table T
-- go
-- Create XML schema collection
-- DROP XML SCHEMA COLLECTION SC
-- go
CREATE XML SCHEMA COLLECTION SC AS '
<schema xmlns="http://www.w3.org/2001/XMLSchema">
      <element name="root" type="QName" nillable="true"/>
</schema>'
go
 -- Create table T with a typed xml column (using the XML schema collection)
CREATE TABLE T (xmlCol XML(SC))
go
-- Insert an XML instance.
insert into T values ('<root xmlns:a="http://someURI">a:b</root>')
 go
-- Verify
SELECT * 
FROM T

The following attempt adds another <root> element but fails, because the expanded-QName() function is not supported in XML construction.

update T SET xmlCol.modify('
insert <root>{expanded-QName("http://ns","someLocalName")}</root> as last into / ')
go

A solution to this is to first insert an instance with a value for the <root> element and then modify it. In this example, a nil initial value is used when the <root> element is inserted. The XML schema collection in this example allows a nil value for the <root> element.

update T SET xmlCol.modify('
insert <root xsi:nil="true"/> as last into / ')
go
-- now replace the nil value with another QName.
update T SET xmlCol.modify('
replace value of /root[last()] with expanded-QName("http://ns","someLocalName") ')
go
 -- verify 
SELECT * FROM T
go
-- result
<root>b</root>

<root xmlns:a="http://someURI">a:b</root>

<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p1="http://ns">p1:someLocalName</root>

You can compare the QName value, as shown in the following query. The query returns only the <root> elements whose values match the QName type value returned by the expanded-QName() function.

SELECT xmlCol.query('
    for $i in /root
    return
       if ($i eq expanded-QName("http://ns","someLocalName") ) then
          $i
       else
          ()')
FROM T

There is one limitation: The expanded-QName() function accepts the empty sequence as the second argument and will return empty instead of raising a run-time error when the second argument is incorrect.