delphi xpath xml query

Question

I\'m trying to locate the value for in the following XML File using a XPath query.

Answer 1

Martijn mentioned about the Vendor property in a comment to his answer.

The property is in fact called DOMVendor.

Further below is some sample code that shows how that works.
The sample code depends on some helper classes you can find on bo.codeplex.com.

Note that DOMVendor will not tell you what version of MSXML you have, but you can ask it if it has XPath support.

Old MSXML versions (that are still in the field, for instance on plain vanilla Windows 2003 Server installations) won't support XPath, but support XSLPattern.
They will happily execute your queries, but sometimes return different results, or barf.

There are some sublte bugs in various sub-versions of MSXML6 too.
You need 6.30., 6.20.1103., 6.20.2003.0 or higher. 6.3 is only available on Windows 7/Windows 2008 Server. The 6.20 flavours on Windows XP and Windows 2003 Server.
Finding out which versions actually work took me a quite some time :-)

This shows you the installed MSXML, in my case msxml6.dll: 6.20.1103.0:

procedure TMainForm.ShowMsxml6VersionClick(Sender: TObject);
begin
{
Windows 2003 with MSXML 3: msxml3.dll: 8.100.1050.0

windows XP with MSXML 4: msxml4.dll: 4.20.9818.0

Windows XP with MSXML 6 SP1: msxml6.dll: 6.10.1129.0

windows XP with MSXML 6 SP2 (latest):
------------------------
msxml6.dll: 6.20.1103.0

Windows 7 with MSXML 6 SP3:
--------------------------
msxml6.dll: 6.30.7600.16385
}
  try
    Logger.Log(TmsxmlFactory.msxmlBestFileVersion.ToString());
    TmsxmlFactory.AssertCompatibleMsxml6Version();
  except
    on E: Exception do
    begin
      Logger.Log('Error');
      Logger.Log(E);
    end;
  end;
end;

This shows the DOMVendor code, it makes some use of helper classes, you can find that on

procedure TMainForm.FillDomVendorComboBox;
var
  DomVendorComboBoxItemsCount: Integer;
  Index: Integer;
  CurrentDomVendor: TDOMVendor;
  DefaultDomVendorIndex: Integer;
  CurrentDomVendorDescription: string;
const
  NoSelection = -1;
begin
  DomVendorComboBox.Clear;
  DefaultDomVendorIndex := NoSelection;
  for Index := 0 to DOMVendors.Count - 1 do
  begin
    CurrentDomVendor := DOMVendors.Vendors[Index];
    LogDomVendor(CurrentDomVendor);
    CurrentDomVendorDescription := CurrentDomVendor.Description;
    DomVendorComboBox.Items.Add(CurrentDomVendorDescription);
    if DefaultDOMVendor = CurrentDomVendorDescription then
      DefaultDomVendorIndex := DomVendorComboBox.Items.Count - 1;
  end;
  DomVendorComboBoxItemsCount := DomVendorComboBox.Items.Count;
  if (DefaultDomVendorIndex = NoSelection) then
  begin
    if DefaultDOMVendor = NullAsStringValue then
    begin
      if DomVendorComboBoxItemsCount > 0 then
        DefaultDomVendorIndex := 0;
    end
    else
      DefaultDomVendorIndex := DomVendorComboBoxItemsCount - 1;
  end;
  DomVendorComboBox.ItemIndex := DefaultDomVendorIndex;
end;

procedure TMainForm.LogDomVendor(const CurrentDomVendor: TDOMVendor);
var
  CurrentDomVendorDescription: string;
  DocumentElement: IDOMElement;
  DomDocument: IDOMDocument; // xmldom.IDOMDocument is the plain XML DOM
  XmlDocument: IXMLDocument; // XMLIntf.IXMLDocument is the enrichted XML interface to the TComponent wrapper, which has a DOMDocument: IDOMDocument poperty, and allows obtaining XML from different sources (text, file, stream, etc)
  XmlDocumentInstance: TXMLDocument; // unit XMLDoc

  DOMNodeEx: IDOMNodeEx;
  XMLDOMDocument2: IXMLDOMDocument2;
begin
  CurrentDomVendorDescription := CurrentDomVendor.Description;
  Logger.Log('DOMVendor', CurrentDomVendorDescription);

  XmlDocumentInstance := TXMLDocument.Create(nil);
  XmlDocumentInstance.DOMVendor := CurrentDomVendor;
  XmlDocument := XmlDocumentInstance;

  DomDocument := CurrentDomVendor.DOMImplementation.createDocument(NullAsStringValue, NullAsStringValue, nil);

  XmlDocument.DOMDocument := DomDocument;
  XmlDocument.LoadFromXML('');
  DomDocument := XmlDocument.DOMDocument; // we get another reference here, since we loaded some XML now

  DocumentElement := DomDocument.DocumentElement;
  if Assigned(DocumentElement) then
  begin
    DOMNodeEx := DocumentElement as IDOMNodeEx;
    Logger.Log(DOMNodeEx.xml);
  end;

  if IDomNodeHelper.GetXmlDomDocument2(DomDocument, XMLDOMDocument2) then
  begin
    // XSLPattern versus XPath
    // see https://stackoverflow.com/questions/784745/accessing-comments-in-xml-using-xpath
    // XSLPattern is 0 based, but XPath is 1 based.
    Logger.Log(IDomNodeHelper.SelectionLanguage, string(XMLDOMDocument2.getProperty(IDomNodeHelper.SelectionLanguage)));
    Logger.Log(IDomNodeHelper.SelectionNamespaces, string(XMLDOMDocument2.getProperty(IDomNodeHelper.SelectionNamespaces)));
  end;


  LogDomVendorFeatures(CurrentDomVendor,
    ['','1.0','2.0', '3.0'],
//http://www.w3.org/TR/DOM-Level-3-Core/introduction.html#ID-Conformance
//http://reference.sitepoint.com/javascript/DOMImplementation/hasFeature
['Core'
,'XML'
,'Events'
,'UIEvents'
,'MouseEvents'
,'TextEvents'
,'KeyboardEvents'
,'MutationEvents'
,'MutationNameEvents'
,'HTMLEvents'
,'LS'
,'LS-Async'
,'Validation'
,'XPath'
]);
end;


procedure TMainForm.LogDomVendorFeatures(const CurrentDomVendor: TDOMVendor; const Versions, Features: array of string);
var
  AllVersions: string;
  Feature: string;
  Line: string;
  Supported: Boolean;
  SupportedAll: Boolean;
  SupportedNone: Boolean;
  SupportedVersions: IStringListWrapper;
  Version: string;
begin
  SupportedVersions := TStringListWrapper.Create();
  for Version in Versions do
    AddSupportedVersion(Version, SupportedVersions);
  AllVersions := Format('All: %s', [SupportedVersions.CommaText]);
  for Feature in Features do
  begin
    SupportedAll := True;
    SupportedNone := True;
    SupportedVersions.Clear();
    for Version in Versions do
    begin
      Supported := CurrentDomVendor.DOMImplementation.hasFeature(Feature, Version);
      if Supported then
        AddSupportedVersion(Version, SupportedVersions);
      SupportedAll := SupportedAll and Supported;
      SupportedNone := SupportedNone and not Supported;
    end;
    if SupportedNone then
      Line := Format('None', [])
    else
    if SupportedAll then
      Line := Format('%s', [AllVersions])
    else
      Line := Format('%s', [SupportedVersions.CommaText]);
    Logger.Log('  ' + Feature, Line);
  end;
end;

Delphi XE will show these:

DOMVendor:MSXML

SelectionLanguage:XPath
SelectionNamespaces:
  Core:None
  XML:Any,1.0
  Events:None
  UIEvents:None
  MouseEvents:None
  TextEvents:None
  KeyboardEvents:None
  MutationEvents:None
  MutationNameEvents:None
  HTMLEvents:None
  LS:None
  LS-Async:None
  Validation:None
  XPath:Any,1.0
DOMVendor:ADOM XML v4
?

  Core:None
  XML:None
  Events:None
  UIEvents:None
  MouseEvents:None
  TextEvents:None
  KeyboardEvents:None
  MutationEvents:None
  MutationNameEvents:None
  HTMLEvents:None
  LS:None
  LS-Async:None
  Validation:None
  XPath:None