Re: Random access of XML file

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From: Stuart Celarier (stuart)
Date: 11/14/04

  • Next message: Victor Hadianto: "Re: Sending Word Document as an attachement." 
    Date: Sat, 13 Nov 2004 18:10:41 -0800

    As Martin suggested, you can use the XmlNode.SelectNodes method [1] to
    select all nodes matching an XPath expression [2]. XmlNode.SelectSingleNode
    selects the first node (in document order) that matches the XPath
    expression.

    The XmlDocument.GetElementByID method requires use of a DTD to identify
    which attributes are treated as IDs [3]. DTDs are very nearly dead, and you
    are better served in the long term by not relying on them.

    If your document is not well-formed XML, then all bets are off.
    Fundamentally, if it's not well-formed XML, then it isn't XML, period. In
    the case of XmlDocument, you can't load a document that is not well-formed
    XML.

    If you want to go a step further beyond XPath support (SelectNodes), you can
    look at XSLT [4], but that may be overkill depending on your needs. The XSLT
    element <xsl:key> acts like an index over the XML source document, and the
    key() function acts like a SELECT statement over that index. This has the
    potential of delivering better performance.

    Here is a key that indexes all elements having at least one attribute whose
    name contains the string 'ID', indexed by the values of any such attributes.

    <xsl:key name="AllIDs"
        match="*[contains(local-name(@*), 'ID')]"
        use="@*[contains(local-name(.), 'ID')]"/>

    That key can be used in expressions in XSLT elements like this

    key('AllIDs', '3')

    This selects all elements anywhere in the document that have at least one
    attribute whose name contains the string 'ID' and whose value is 3. (Caveat,
    I'm just writing this XSLT off the top of my head to give you the flavor.)

    I should point out that XSLT is a general purpose transform language for XML
    and can take a while to learn. It may be much more than you need or are
    willing to undertake.

    Cheers,
    Stuart Celarier, Fern Creek

    [1]
    http://msdn.microsoft.com/library/en-us/cpref/html/frlrfsystemxmlxmlnodeclassselectnodestopic1.asp
    [2] http://www.w3.org/TR/1999/REC-xpath-19991116
    [3]
    http://msdn.microsoft.com/library/en-us/cpref/html/frlrfsystemxmlxmldocumentclassgetelementbyidtopic.asp
    [4] http://www.w3.org/TR/1999/REC-xslt-19991116

  • Next message: Victor Hadianto: "Re: Sending Word Document as an attachement."

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