unit1.~pas

使用ADO进行二进制字段读写的一个例子

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  Db, ADODB, StdCtrls, Grids, DBGrids, ExtCtrls, DBCtrls, ComCtrls;

type
  TForm1 = class(TForm)
    ADOConnection1: TADOConnection;
    ADOTable1: TADOTable;
    DBGrid1: TDBGrid;
    DataSource1: TDataSource;
    SaveDialog1: TSaveDialog;
    Panel1: TPanel;
    Button1: TButton;
    DBNavigator1: TDBNavigator;
    StatusBar1: TStatusBar;
    Button2: TButton;
    TableNameComboBox: TComboBox;
    Button3: TButton;
    OpenDialog: TOpenDialog;
    procedure Button1Click(Sender: TObject);
    procedure DBGrid1CellClick(Column: TColumn);
    procedure ADOConnection1AfterConnect(Sender: TObject);
    procedure TableNameComboBoxChange(Sender: TObject);
    procedure ADOConnection1BeforeDisconnect(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
    FColumn: TColumn;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
var
  F: TFileStream;
  Stream: TStream;
begin
  if SaveDialog1.Execute and (FColumn<>nil)and(FColumn.Field <> nil)and(FColumn.Field.IsBlob)  then
  begin
    with ADOTable1 do
    begin
      Stream := CreateBlobStream(FColumn.Field, bmRead);
      try
        F := TFileStream.Create(SaveDialog1.FileName, fmCreate);
        try
          F.CopyFrom(Stream, Stream.Size);
        finally
          F.Free;
        end;
      finally
        Stream.Free;
      end;
    end;
  end;
end;

procedure TForm1.DBGrid1CellClick(Column: TColumn);
begin
  FColumn := Column;
end;

procedure TForm1.ADOConnection1AfterConnect(Sender: TObject);
begin
  (Sender as TADOConnection).GetTableNames(TableNameComboBox.Items);
end;

procedure TForm1.TableNameComboBoxChange(Sender: TObject);
begin
  ADOTable1.DisableControls;
  try
    ADOTable1.Active := False;
    ADOTable1.TableName := (Sender as TComboBox).Text;
    ADOTable1.Active := True;
  finally
    ADOTable1.EnableControls;
  end;
end;

procedure TForm1.ADOConnection1BeforeDisconnect(Sender: TObject);
begin
  if TableNameComboBox<> nil then
  TableNameComboBox.Items.Clear;
end;

procedure TForm1.Button2Click(Sender: TObject);
var
  S: string;
begin
  S := ADODB.PromptDataSource(Handle, ADOConnection1.ConnectionString);
  if S <> ADOConnection1.ConnectionString then
  begin
    ADOConnection1.Connected := False;
    ADOConnection1.ConnectionString := S;
    ADOConnection1.Connected := True;
  end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  TableNameComboBox.Free;
  TableNameComboBox := nil;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
  F: TFileStream;
  Stream: TStream;
begin
  if (FColumn<>nil)and(FColumn.Field <> nil)and(FColumn.Field.IsBlob) then
  if OpenDialog.Execute then
  begin
    with ADOTable1 do
    begin
      Edit;
      F := TFileStream.Create(OpenDialog.FileName, fmOpenRead);
      try
        Stream := CreateBlobStream(FColumn.Field, bmRead);
        try
          Stream.Size := 0;
          Stream.CopyFrom(F, 0)
        finally
          Stream.Free;
        end;
      finally
        F.Free;
      end;
      Post;
    end;
  end;
end;

end.