Manter Dataset aberto condicionalmente

dmLocal := TDataModule.Create(Self);

dmLocal := Tdmtabelas.Create(Self);

//Project1.dpr

program Project1;

uses
  Forms,
  Unit1 in ´Unit1.pas´ ,
  Unit2 in ´Unit2.pas´ {DataModule1: TDataModule};

{$R *.RES}

var
  Form1: TForm1;
begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

//Form...

//Unit1.pas

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, Unit2, Grids, DBGrids;

type
  TForm1 = class(TForm)

    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
    DataModule1: TDataModule1;
  public
    { Public declarations }
  end;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  DataModule1 := TDataModule1.Create(nil);
  DataSource1.DataSet := DataModule1.ADODataSet1;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  DataModule1.Free;
end;

end.

//Unit1.DFM

object Form1: TForm1
  Left = 192
  Top = 107
  Width = 696
  Height = 480
  Caption = ´Form1´
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  object DBGrid1: TDBGrid
    Left = 4
    Top = 4
    Width = 320
    Height = 120
    DataSource = DataSource1
  end
  object DataSource1: TDataSource
    Left = 328
    Top = 4
  end
end

//Data module...
//Unit2.pas

unit Unit2;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, ADODB;

type
  TDataModule1 = class(TDataModule)
    ADOConnection1: TADOConnection;
    ADODataSet1: TADODataSet;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

implementation

{$R *.DFM}

end.

//Unit2.DFM

object DataModule1: TDataModule1
  Left = 272
  Top = 162
  Height = 480
  Width = 696
  object ADOConnection1: TADOConnection
    Left = 40
    Top = 20
  end
  object ADODataSet1: TADODataSet
    Connection = ADOConnection1
    Left = 124
    Top = 20
  end
end

//dpr
program Project1;

uses
  Forms,
  Unit1 in ´Unit1.pas´ ,
  Unit2 in ´Unit2.pas´ {DataModule1: TDataModule},
  Unit3 in ´Unit3.pas´;

{$R *.RES}

var
  Form1: TForm1;
begin
  Application.Initialize;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

//pas
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, Grids, DBGrids, Unit3;

type
  TForm1 = class(TForm)
    DataSource1: TDataSource;
    DBGrid1: TDBGrid;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure FormShow(Sender: TObject);
  private
    { Private declarations }
    Negocio1: TNegocio1;
  public
    { Public declarations }
  end;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Negocio1 := TNegocio1.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Negocio1.Free;
end;

procedure TForm1.FormShow(Sender: TObject);
begin
  DataSource1.DataSet := Negocio1.Abre;
end;

end.

//dfm
object Form1: TForm1
  Left = 192
  Top = 107
  Width = 696
  Height = 480
  Caption = ´Form1´
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = ´MS Sans Serif´
  Font.Style = []
  OldCreateOrder = True
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  OnShow = FormShow
  PixelsPerInch = 96
  TextHeight = 13
  object DBGrid1: TDBGrid
    Left = 4
    Top = 4
    Width = 320
    Height = 120
    DataSource = DataSource1
    TabOrder = 0
    TitleFont.Charset = DEFAULT_CHARSET
    TitleFont.Color = clWindowText
    TitleFont.Height = -11
    TitleFont.Name = ´MS Sans Serif´
    TitleFont.Style = []
  end
  object DataSource1: TDataSource
    Left = 328
    Top = 4
  end
end

//pas
unit Unit2;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, DbClient, ADODB, Provider;

type
  TDataModule1 = class(TDataModule)
    ADOConnection1: TADOConnection;
    ADODataSet1: TADODataSet;
    ClientDataSet1: TClientDataSet;
    DataSetProvider1: TDataSetProvider;
  private
    { Private declarations }
  public
    { Public declarations }
  end;

implementation

{$R *.DFM}

end.

//dfm
object DataModule1: TDataModule1
  OldCreateOrder = True
  Left = 272
  Top = 162
  Height = 480
  Width = 696
  object ADOConnection1: TADOConnection
    Left = 40
    Top = 20
  end
  object ADODataSet1: TADODataSet
    Connection = ADOConnection1
    Parameters = <>
    Left = 124
    Top = 20
  end
  object ClientDataSet1: TClientDataSet
    Aggregates = <>
    Params = <>
    ProviderName = ´DataSetProvider1´
    Left = 292
    Top = 20
  end
  object DataSetProvider1: TDataSetProvider
    DataSet = ADODataSet1
    Constraints = True
    UpdateMode = upWhereKeyOnly
    Left = 208
    Top = 20
  end
end

//pas
unit Unit3;

interface

uses
  DbClient, Unit2;

type
  TNegocio1 = class(TObject)
  private
    DataModule1: TDataModule1;    
  public
    constructor Create; 
    destructor Destroy; override;
    function Abre: TClientDataSet;
    procedure Fecha;
  end;

implementation

function TNegocio1.Abre: TClientDataSet;
begin
  DataModule1.ClientDataSet1.Close;
  DataModule1.ADODataSet1.CommandText := ´SELECT...´;
  DataModule1.ClientDataSet1.Open;
  Result := DataModule1.ClientDataSet1;
end;

procedure TNegocio1.Fecha;
begin
  DataModule1.ClientDataSet1.Close;
end;

constructor TNegocio1.Create;
begin
  DataModule1 := TDataModule1.Create(nil);
end;

destructor TNegocio1.Destroy;
begin
  DataModule1.Free;
  inherited;
end;

end.