main.pas

Delphi7数据库开发教程,包含该书21套实例

unit main;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, DB, ADODB;

type
  TForm1 = class(TForm)
    ADOConnection1: TADOConnection;
    Label1: TLabel;
    btnBeginTrans: TButton;
    btnCommitTrans: TButton;
    btnRollbackTrans: TButton;
    btnClose: TButton;
    procedure btnBeginTransClick(Sender: TObject);
    procedure btnCloseClick(Sender: TObject);
    procedure btnRollbackTransClick(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure btnCommitTransClick(Sender: TObject);
  private
    { Private declarations }
    TransLevel:Integer;
    procedure DisplayTransLevel;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.btnBeginTransClick(Sender: TObject);
begin
  With ADOConnection1 do
    TransLevel := BeginTrans;
  DisplayTransLevel;
end;

procedure TForm1.btnCloseClick(Sender: TObject);
begin
  Close;           //
end;

procedure TForm1.btnRollbackTransClick(Sender: TObject);
begin
  //如果还不是最后一个事务，则回滚事务
  With ADOConnection1 do
  begin
    if InTransaction then
    begin
      RollbackTrans;
      Dec(TransLevel) ;
      DisplayTransLevel;
    end
    else
      ShowMessage('没有开始新的事务，不能回滚操作');
  end;    
end;

//自定义方法，用于显示当前的事务嵌套等级
procedure TForm1.DisplayTransLevel;
begin
  Label1.Caption := '当前的事务嵌套等级：' + IntToStr(TransLevel);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  //初始化参数，当前事务数为0
  TransLevel := 0;
end;

procedure TForm1.btnCommitTransClick(Sender: TObject);
begin
  //如果还不是最后一个事务，则提交事务
  With ADOConnection1 do
  begin
    if InTransaction then
    begin
      CommitTrans;
      Dec(TransLevel) ;
      DisplayTransLevel;
    end
    else
      ShowMessage('没有开始新的事务，不能提交操作');
  end;
end;

end.