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XML Path Performance Optimizations

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

Local $bSuccess = False

$oXml = ObjCreate("Chilkat.Xml")

;  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>
;  
$bSuccess = $oXml.LoadXmlFile("qa_output/large.xml")
If ($bSuccess <> True) Then
    ConsoleWrite($oXml.LastErrorText & @CRLF)
    Exit
EndIf

;  Iterating over the individual "license" nodes with this code snippet is
;  extremely slow:
Local $iLicCount = $oXml.NumChildrenHavingTag("licenses|license")
ConsoleWrite("license count = " & $iLicCount & @CRLF)

Local $s
Local $i = 0
;  If "10" is changed to licCount, then it becomes apparent that this loop gets slower with each iteration.
While $i < 10
    $oXml.I = $i
    $s = $oXml.GetChildContent("licenses|license[i]|id")
    ConsoleWrite($i & ": " & $s & @CRLF)
    $i = $i + 1
Wend

;  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:

$i = 0
;  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
    $oXml.I = $i
    $s = $oXml.GetChildContent("licenses|[i]|id")
    ConsoleWrite($i & ": " & $s & @CRLF)
    $i = $i + 1
Wend

;  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:
$iLicCount = $oXml.NumChildrenAt("licenses")
ConsoleWrite("licCount = " & $iLicCount & @CRLF)

;  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.