Delphi XML Recursive function, search a node with specific attribute value

Question

I try to find a node with specific "node name", "attribute" and "attribute value". I use the recursive function below.

My XMLDocument has a node named 'TestNodeName' with attribute 'Format' with value '1'.

The function works fine the first time: returns the prower node.
When I call it a second time, it gives wrong results: returns a node that has a Format attribute having value 0.

Example of XML.

<mnode>
  <TestNodeName ID="1" Format="0">
  </TestNodeName>
  <TestNodeName ID="2" Format="1">
  </TestNodeName>
  <TestNodeName ID="3" Format="0">
  </TestNodeName>
  <TestNodeName ID="4" Format="1">
  </TestNodeName>
  <TestNodeName ID="5" Format="0">
  </TestNodeName>
</mnode>

End of XML

unit Unit4;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, XMLIntf, XMLDoc;

type
  TForm4 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
//GLOBAL VARIABLES
var
  Form4: TForm4;
  XML:IXMLDocument;
  mnode:IXMLNode;
  s:string;
implementation

{$R *.dfm}
function RecursiveFindNode(ANode: IXMLNode; const SearchNodeName: string): IXMLNode;
var
  I: Integer;
begin
  if CompareText(ANode.NodeName, SearchNodeName) = 0 then
    Result := ANode
  else if not Assigned(ANode.ChildNodes) then
    Result := nil
  else begin
    for I := 0 to ANode.ChildNodes.Count - 1 do
    begin
      Result := RecursiveFindNode(ANode.ChildNodes[I], SearchNodeName);
      if Assigned(Result) then
        Exit;
    end;
  end;
end;

function RecursiveFindNodeAttr(ANode: IXMLNode; const SearchNodeName: string; sAttr, sAttrVal:string): IXMLNode;
var
  I: Integer;
  sAttrFind: ixmlnode;
  stext:string;
begin
  sAttrFind:=ANode.AttributeNodes.FindNode(sAttr);
  if sAttrFind<>nil then stext:=sAttrFind.Text else stext:='';
  if (CompareText(ANode.NodeName, SearchNodeName)=0)and(CompareText(sAttrFind.NodeName, sAttr)=0)and(CompareText(stext, sAttrVal)=0) then
  begin
    Result := ANode;
  end
  else if not Assigned(ANode.ChildNodes) then
  begin
    Result := nil;
  end
  else begin
    for I := 0 to ANode.ChildNodes.Count - 1 do
    begin
      Result := RecursiveFindNodeAttr(ANode.ChildNodes[I], SearchNodeName, sAttr, sAttrVal);
      if Assigned(Result) then
      begin
        Exit;
      end;
    end;
  end;
end;

procedure TForm4.FormCreate(Sender: TObject);
var
cnode,foundNode:IXMLNode; //<-- Problem here "foundNode" must be in global 
begin
XML:= NewXMLDocument;
XML.LoadFromFile('C:\test.xml');
mnode:=XML.DocumentElement;
foundNode:=RecursiveFindNode(mnode,'TestNodeName');

//First time
cnode:=RecursiveFindNodeAttr(XML.DocumentElement,'TestNodeName','Format','1');
if cnode<>nil then
begin
cnode.Attributes['Format']:='5';
ShowMessage('ID='+cnode.Attributes['ID']);
end
else
ShowMessage('nil');

//Second time
foundNode:=RecursiveFindNodeAttr(XML.DocumentElement,'TestNodeName','Format','1');
if foundNode<>nil then
begin
foundNode.Attributes['Format']:='5';
ShowMessage('ID='+foundNode.Attributes['ID']);
end
else
ShowMessage('nil');

XML.SaveToFile('C:\test.xml');


end;

end.

After few test i finally found what caused wrong result of function. There was a similar recursive function. When i removed call of function all result was OK. RecursiveFindNode(ANode: IXMLNode; const SearchNodeName: string): IXMLNode;

In code bellow is call foundNode:=RecursiveFindNode(mnode,'TestNodeName'); The first call of RecursiveFindNodeAttr will give good result because of "cnode:=" The second call of RecursiveFindNodeAttr will give wrong result (ID=1) because i used same variable "foundNode:=RecursiveFindNodeAttr(..."

Finally when i moved "var foundNode:IXMLNode;" from Tform4 declaration to global the second call returned good result (ID=4)

I found another problem. when i use RecursiveFindNodeAttr in loop after replace all format="1" to format="5", the "foundNode" result remains "not nil" so loop will never end.

foundNode:=RecursiveFindNodeAttr(XML.DocumentElement,'TestNodeName','Format','1');
while foundNode<>nil do
begin
    foundNode.Attributes['Format']:='5';
    ShowMessage('ID='+foundNode.Attributes['ID']);

foundNode:=RecursiveFindNodeAttr(XML.DocumentElement,'TestNodeName','Format','1');
if foundNode=nil then ShowMessage('nil');
end;

Answer 1

I found already made function which work fine with IXMLDocument. Function returns list of nodes if match parameters. XML is same as above (the one with "UID" attributes)

//Declared funciton
function FindNodeList(xnRoot: IXmlNode; const nodePath: WideString): IXMLNodeList;
var
   intfSelect : IDomNodeSelect;
   intfAccess : IXmlNodeAccess;
   dnlResult  : IDomNodeList;
   intfDocAccess : IXmlDocumentAccess;
   doc: TXmlDocument;
   i : Integer;
   dn : IDomNode;
begin
   Result := nil;
   if not Assigned(xnRoot)
     or not Supports(xnRoot, IXmlNodeAccess, intfAccess)
     or not Supports(xnRoot.DOMNode, IDomNodeSelect, intfSelect) then
     Exit;

   dnlResult := intfSelect.selectNodes(nodePath);
   if Assigned(dnlResult) then
   begin
     Result := TXmlNodeList.Create(intfAccess.GetNodeObject, '', nil);
     if Supports(xnRoot.OwnerDocument, IXmlDocumentAccess, intfDocAccess) then
       doc := intfDocAccess.DocumentObject
     else
       doc := nil;

     for i := 0 to dnlResult.length - 1 do
     begin
       dn := dnlResult.item[i];
       Result.Add(TXmlNode.Create(dn, nil, doc));
     end;
   end;
end;

---

var
  xlist:IXMLNodeList;
  mnode:IXMLNode;
  XML:IXMLDocument;
begin
  XML:= NewXMLDocument;
  XML.LoadFromFile('C:\test.xml');
  mnode:=XML.DocumentElement;

  //This will find all nodes in nodes and subnodes if node name is "TestNodeName" attribute Format="1"
  xlist:=FindNodeList(mnode,'//TestNodeName[@Format="1"]');
  for I := 0 to xlist.Count - 1 do
    begin
      //This will set Format value to "8"
      xlist[i].Attributes['Format']:='8';
    end;


end.

Answer 2

It seems "if not Assigned(ANode.ChildNodes) then" is always assigned. when i changed it to "if not (ANode.HasChildNodes) then" it stopped loop forever. I added into function messages to display how exactly is function executed.

It seems it checks same node 2 times, 1st time in "if (CompareText(ANode.Node..." and second time in loop "for I := 0 to ANode.ChildNo...".

<mnode UID="main">
  <TestNodeName UID="1" Format="5">
    <TestNodeName UID="11" Format="5">
    </TestNodeName>
    <TestNodeName UID="12" Format="5">
    </TestNodeName>
    <TestNodeName UID="13" Format="5">
    </TestNodeName>
  </TestNodeName>
  <TestNodeName UID="2" Format="5">
  </TestNodeName>
  <TestNodeName UID="3" Format="5">
    <TestNodeName UID="31" Format="5">
    </TestNodeName>
    <TestNodeName UID="32" Format="5">
      <TestNodeName UID="321" Format="1">
      </TestNodeName>
      <TestNodeName UID="322" Format="5">
      </TestNodeName>
      <TestNodeName UID="323" Format="1">
      </TestNodeName>
    </TestNodeName>
    <TestNodeName UID="33" Format="5">
    </TestNodeName>
  </TestNodeName>
  <TestNodeName UID="4" Format="5">
  </TestNodeName>
</mnode>

---

function RecursiveFindNodeAttr(ANode: IXMLNode; const SearchNodeName: string; sAttr, sAttrVal:string): IXMLNode;
var
  I: Integer;
begin
  if (CompareText(ANode.NodeName, SearchNodeName)=0)and(ANode.Attributes[sAttr]=sAttrVal) then
  begin
    ShowMessage('Found! '+ANode.Attributes['UID']);
    Result := ANode;
  end
  else
    begin
    ShowMessage('1st try='+ANode.Attributes['UID']);
    if not (ANode.HasChildNodes) then
    begin
    ShowMessage('nil');
    Result := nil;
    end
  else begin
    for I := 0 to ANode.ChildNodes.Count - 1 do
     begin
      Result := RecursiveFindNodeAttr(ANode.ChildNodes[I], SearchNodeName, sAttr, sAttrVal);
      ShowMessage('loop='+ANode.ChildNodes[I].Attributes['UID']);
      if Assigned(Result) then
      begin
        ShowMessage('found in loop='+ANode.ChildNodes[I].Attributes['UID']);
        Exit;
      end;
     end;
    end;
   end;
end;

---

var
  XML:IXMLDocument;
  mnode,cnode:IXMLNode;

begin

XML:= NewXMLDocument;
XML.LoadFromFile('C:\test.xml');
mnode:=XML.DocumentElement;

//This will replace all Format="1" to Format="0"
cnode:=RecursiveFindNodeAttr(mnode,'TestNodeName','Format','1');
while cnode<>nil do
begin
  cnode.Attributes['Format'] := '0';
  ShowMessage(cnode.Attributes['UID']);
  cnode:=RecursiveFindNodeAttr(mnode,'TestNodeName','Format','1');
end;
if cnode= nil  then
ShowMessage('cnode= nil ');

end.