DELPHI存取JPEG文件到SQL Server数据库

作者：高红岩　来源：programfan.com　http://www.csai.cn　2006年03月16日
　　近日笔者书写一个小型的学生管理系统时，需要用到ADO控件存取SQL Server数据库图片，查看资料发现基本都是针对BMP文件进行操作(巨增数据库大小)，但发现了eagletian高手翻译的ADO英文技术文档，里面涉及到了数据库存取JPEG文件的关键技术，在win98+sql server桌面版中测试通过，运行良好，现于源码公开如下：

unit Unit1;
interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  ExtCtrls, DBCtrls, Grids, DBGrids, Db, ADODB,jpeg, StdCtrls,dbtables;
{一定要USES JPEG单元,使能存储JPG文件格式}
type
  TForm1 = class(TForm)
  DataSource1: TDataSource;
  ADOQuery1: TADOQuery;
  DBGrid1: TDBGrid;
  DBNavigator1: TDBNavigator;
  Image1: TImage;
  savebutton: TButton;
  showbutton: TButton;
  OpenDialog1: TOpenDialog;
  ADOQuery1id: TIntegerField;
  ADOQuery1pic: TBlobField;
procedure savebuttonClick(Sender: TObject);
procedure showbuttonClick(Sender: TObject);
procedure DBNavigator1Click(Sender: TObject; Button: TNavigateBtn);
private
{ Private declarations }
public
{ Public declarations }
end;

var
Form1: TForm1;

implementation

{$R *.DFM}

function JpegStartsInBlob(PicField:TBlobField):integer;
var
  ghy: TADOBlobstream;
  buffer:Word;
  hx: string;
begin
  Result := -1;
  ghy := TADOBlobstream.Create(PicField, bmRead);
  try
    while (Result = -1) and (ghy.Position + 1 < ghy.Size) do
    begin
      ghy.ReadBuffer(buffer, 1);
      hx:=IntToHex(buffer, 2);
      if hx = ’FF’ then
      begin
        ghy.ReadBuffer(buffer, 1);
        hx:=IntToHex(buffer, 2);
        if hx = ’D8’ then
          Result := ghy.Position - 2
        else if hx = ’FF’ then
          ghy.Position := ghy.Position-1;
      end; //if
    end; //while
  finally
    ghy.Free
  end; //try
end;

procedure TForm1.savebuttonClick(Sender: TObject);
var
  picstream:tadoblobstream;
begin
  adoquery1.edit;
  picstream:=tadoblobstream.Create(tblobfield(adoquery1.fields[1]),bmWrite);
  if form1.opendialog1.execute then
  begin
    picstream.LoadFromFile(opendialog1.filename);
    picstream.Position:=0;
    adoquery1.edit;
    tblobfield(adoquery1.Fields[1]).loadfromstream(picstream);
    adoquery1.post;
  end;
end;

procedure TForm1.showbuttonClick(Sender: TObject);
var
  ghy:TADOBlobstream;
  pic:tjpegimage;
begin
  ghy := TADOBlobstream.Create(Adoquery1pic, bmRead);
  try
    ghy.Seek(JpegStartsInBlob(Adoquery1pic),soFromBeginning);
    Pic:=TJpegImage.Create;
    try
      Pic.LoadFromStream(ghy);
      Image1.Picture.Graphic:=Pic;
    finally
      Pic.Free;
    end;
  finally
    ghy.Free
  end;
end;

procedure TForm1.DBNavigator1Click(Sender: TObject; Button: TNavigateBtn);
begin
  if button in [nbFirst, nbPrior, nbNext, nbLast] then showbutton.Click;
end;

//如果数据库中要存储的是BMP文件，则在procedure TForm1.showbuttonClick(Sender: TObject);过程中代码更改如下即可存储显示BMP文件格式的操作。
procedure TForm1.showbuttonClick(Sender: TObject);
var
  ghy:TADOBlobstream;
  pic:tbitmap;
begin
  ghy := TADOBlobstream.Create(Adoquery1pic, bmRead);
  try
    { ghy.Seek(JpegStartsInBlob(Adoquery1pic),soFromBeginning);}
    Pic:=Tbitmap.Create;
    try
      Pic.LoadFromStream(ghy);
      Image1.Picture.Graphic:=Pic;
    finally
      Pic.Free;
    end;
  finally
    ghy.Free
  end;
end;

end.

到此用DELPHI存取JPEG文件到SQL Server数据库中的具体操作已经叙述完毕。