DataFlex

XML Path Performance Optimizations

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Discusses some important things to know about using Chilkat paths in the Chilkat XML API. DataFlex

Use ChilkatAx-win32.pkg

Procedure Test
    Boolean iSuccess
    Handle hoXml
    Integer iLicCount
    String s
    Integer i
    String sTemp1

    Move False To iSuccess

    Get Create (RefClass(cComChilkatXml)) To hoXml
    If (Not(IsComObjectCreated(hoXml))) Begin
        Send CreateComObject of hoXml
    End

    // Let's load XML containing the following:

    // <?xml version="1.0" encoding="utf-8"?>
    // <xyz>
    //     <licenses>
    //         <license>
    //             <id>1234</id>
    //         </license>
    //         <license>
    //             <id>1234</id>
    //         </license>
    // ...
    // My sample XML contains 64,000 "license" nodes ..
    // ...
    //         <license>
    //             <id>1234</id>
    //         </license>
    //         <license>
    //             <id>1234</id>
    //         </license>
    //     </licenses>
    // </xyz>
    // 
    Get ComLoadXmlFile Of hoXml "qa_output/large.xml" To iSuccess
    If (iSuccess <> True) Begin
        Get ComLastErrorText Of hoXml To sTemp1
        Showln sTemp1
        Procedure_Return
    End

    // Iterating over the individual "license" nodes with this code snippet is
    // extremely slow:
    Get ComNumChildrenHavingTag Of hoXml "licenses|license" To iLicCount
    Showln "license count = " iLicCount

    Move 0 To i
    // If "10" is changed to licCount, then it becomes apparent that this loop gets slower with each iteration.
    While (i < 10)
        Set ComI Of hoXml To i
        Get ComGetChildContent Of hoXml "licenses|license[i]|id" To s
        Showln i ": " s
        Move (i + 1) To i
    Loop

    // The reason it is extremely slow is that the "license[i]" part of the path passed to GetChildContent
    // says: find the i'th child of "licenses" having the tag "license".  Chilkat cannot assume that all
    // children of an XML node have the same tag.  Therefore it's not possible to directly access the i'th child.
    // Internally, Chilkat must start at the 1st child and iterate until it reaches the i'th child having the
    // tag "license".

    // For example, imagine if the XML was like this:

    // <?xml version="1.0" encoding="utf-8"?>
    // <xyz>
    //     <licenses>
    //         <license>
    //             <id>1234</id>
    //         </license>
    //         <somethingElse>
    //             <a>abc</a>
    //         </somethingElse>
    //         <license>
    //             <id>1234</id>
    //         </license>
    // ...

    // In the above XML, the 1st "license" is the 1st child of "licenses", but the 2nd "license"
    // is the 3rd child of "licenses".

    // If you already know that all children have the same tag, there is a shortcut that allows
    // for direct access to that child.  Just leave off the tag name, like this:

    Move 0 To i
    // If "10" is changed to licCount, then we can see the time for each loop is the same, and it's fast.
    While (i < 10)
        Set ComI Of hoXml To i
        Get ComGetChildContent Of hoXml "licenses|[i]|id" To s
        Showln i ": " s
        Move (i + 1) To i
    Loop

    // When we pass just the index "[i]", we're saying: Get the i'th child regardless of tag.
    // This is extremely fast because internally we can just access the i'th child directly.

    // Another performance improvement is to call NumChildrenAt rather than NumChildrenHavingTag.
    // For example:
    Get ComNumChildrenAt Of hoXml "licenses" To iLicCount
    Showln "licCount = " iLicCount

    // NumChildrenAt returns the total number of children at the tag path.  If we already know
    // all children will have the same tag, we can just get the count


End_Procedure