Writing n-tier Application for accessing client's app to DataBase without installing Client of Database via 3th server using Indy

This is simple sample how organize work client's app with DataBase without installing Database client or organize remote access to database.

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdTCPServer, IdBaseComponent, IdComponent,
  IdTCPConnection, IdTCPClient, DBClient, Provider, Grids, DBGrids, DB,
  OracleData, Oracle, IdAntiFreezeBase, IdAntiFreeze;

type
  TForm1 = class(TForm)
    OracleSession1: TOracleSession;
    OracleDataSet1: TOracleDataSet;
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    DataSetProvider1: TDataSetProvider;
    ClientDataSet1: TClientDataSet;
    IdTCPClient1: TIdTCPClient;
    IdTCPServer1: TIdTCPServer;
    Button1: TButton;
    Memo1: TMemo;
    IdAntiFreeze1: TIdAntiFreeze;
    procedure Button1Click(Sender: TObject);
    procedure IdTCPServer1Connect(AThread: TIdPeerThread);
    procedure IdTCPServer1Execute(AThread: TIdPeerThread);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
procedure variantToStream(const v: oleVariant; stream: TStream);
var p: pointer;
begin
  stream.position:= 0;
  stream.size:= varArrayHighBound(v,1) - varArrayLowBound(v,1)+1;
  p:= varARrayLock(v);
  stream.write(p^, stream.size);
  varARrayUnlock(v);
  stream.position:= 0;
end;

procedure VarArrayToStream(const Data: OleVariant; Stream: TStream);
var
  p: Pointer;
begin
  p := VarArrayLock(Data);
  try
    Stream.Write(p^, VarArrayHighBound(Data,1) + 1);  //assuming low bound = 0
  finally
    VarArrayUnlock(Data);
  end;
end;

function StreamToVarArray(Stream: TStream): OleVariant;
var
  p: Pointer;
begin
  Result := VarArrayCreate([0, Stream.Size - 1], varByte);
  p := VarArrayLock(Result);
  try
    Stream.Position := 0;  //start from beginning of stream
    Stream.Read(p^, Stream.Size);
  finally
    VarArrayUnlock(Result);
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  ms:TMemoryStream;
begin
ms:=TMemoryStream.Create;
if not IdTCPClient1.Connected then IdTCPClient1.Connect;
if IdTCPClient1.Connected then
  Memo1.Lines.Add('connected')
else
  Memo1.Lines.Add('Not Connected');

IdTCPClient1.Write('open');
IdTCPClient1.ReadStream(ms,STrToINt(IdTCPClient1.ReadString(10)));
ClientDataSet1.Data:=StreamToVarArray(ms);
// ClientDataSet1.LoadFromStream(ms);
ClientDataSet1.Active:=True;
end;

procedure TForm1.IdTCPServer1Connect(AThread: TIdPeerThread);
begin
//
end;

procedure TForm1.IdTCPServer1Execute(AThread: TIdPeerThread);
var
s:string;
ms:TMemoryStream;
begin
with AThread.Connection do begin
  s:=ReadString(4);
  if s='open' then begin
   ms:=TMemoryStream.Create;
   VarArrayToStream(DataSetProvider1.Data,ms);
   s:=IntToSTr(ms.Size);
   while length(s)<10 do begin
    s:='0'+s;
   end;
   Write(s);
   ms.Seek(0,soFromBeginning);

   WriteStream(ms);
  end;
end;
end;

end.