about a function to create a json string.

unit Unit3;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
 
type
  TForm3 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
var
  Form3: TForm3;
 
implementation
 
{$R *.dfm}
 
uses Contnrs;
 
var nSongs: Integer;
 
type
  TFavoritSong = class;
 
  TFavoritSongs = class(TObjectList)
  private
    function GetItems(Index: Integer): TFavoritSong;
    procedure SetItems(Index: Integer; const Value: TFavoritSong);
  protected
  public
    function FindSong(List: TFavoritSongs; aTitle: string): TFavoritSong;
    function JSonString(IsTop: Boolean = True): string;
 
    procedure AddSong(ParentTitle: string; aTitle: string; aCatalog: string = '');
    property Items[Index: Integer]: TFavoritSong read GetItems write SetItems;
  end;
 
  TFavoritSong = class(TObject)
  private
    fId: integer;
    fCatalog: string;
    fTitle: string;
    fFavoritSongs: TFavoritSongs;
  protected
  public
    constructor Create(ATitle: string = ''; ACatalog: string = ''); virtual;
    destructor Destroy; override;
 
    function JSonString: string;
 
    property ID: integer read fID;
    property Title: string read fTitle write fTitle;
    property Catalog: string read fCatalog write fCatalog;
    property Items: TFavoritSongs read fFavoritSongs;
  end;
 
{ TFavoritSong }
 
constructor TFavoritSong.Create(ATitle: string = ''; ACatalog: string = '');
begin
  inherited Create;
  Inc(nSongs);
  fId := nSongs;
  fTitle := aTitle;
  fCatalog := aCatalog;
  fFavoritSongs := TFavoritSongs.Create;
end;
 
destructor TFavoritSong.Destroy;
begin
  fFavoritSongs.Free;
  inherited Destroy;
end;
 
function TFavoritSong.JSonString: string;
begin
  Result :=
    Format('''id'':''%d'',''title'':%s', [Id, QuotedStr(Title)]) +
    Items.JSonString(False);
end;
 
{ TFavoritSongs }
 
function TFavoritSongs.FindSong(List: TFavoritSongs; aTitle: string): TFavoritSong;
var I: integer;
begin
  Result := nil;
  for I := 0 to List.Count - 1 do
    if Result = nil then
    begin
      if SameText(List.Items[I].Title, aTitle) then
      begin
        Result := List.Items[I];
        Break;
      end else
        Result := FindSong(List.Items[I].Items, aTitle);
    end;
end;
 
procedure TFavoritSongs.AddSong(ParentTitle, aTitle, aCatalog: string);
var Parent: TFavoritSong;
begin
  Parent := nil;
  if ParentTitle <> '' then
    Parent := FindSong(Self, ParentTitle);
  if Assigned(Parent) then
    Parent.Items.Add(TFavoritSong.Create(aTitle, aCatalog))
  else
    Add(TFavoritSong.Create(aTitle, aCatalog));
end;
 
function TFavoritSongs.GetItems(Index: Integer): TFavoritSong;
begin
  Result := TFavoritSong(GetItem(Index));
end;
 
function TFavoritSongs.JSonString(IsTop: Boolean): string;
var I: Integer;
  Comma: string;
begin
  Result := '';
  if Count > 0 then
  begin
    if not IsTop then
      Result := Result + ',items:';
    Result := Result + '[';
    Comma := '';
    for I := 0 to Count - 1 do
    begin
      Result := Result +
        Format('%s{%s}', [Comma, Items[I].JSonString]);
      Comma := ',';
    end;
    Result := Result + ']';
  end;
end;
 
procedure TFavoritSongs.SetItems(Index: Integer; const Value: TFavoritSong);
begin
  SetItem(Index, Value);
end;
 
procedure TForm3.Button1Click(Sender: TObject);
var List: TFavoritSongs;
  n, m: Integer;
  item: TFavoritSong;
begin
  nSongs := 0;
  List := TFavoritSongs.Create;
  try
    List.AddSong('', 'title1', '1');
    List.AddSong('', 'title2');
    List.AddSong('', 'title3');
    List.AddSong('title1', 'title4', '1');
    List.AddSong('title4', 'title5');
    List.AddSong('title1', 'title6');
    List.AddSong('title4', 'title7');
    ShowMessage(List.JSonString);
  finally
    List.Free;
  end;
end;
 
end.

                                              

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