DELPHI存取JPEG文件到SQL Server数据库

高红岩（ghyghost）

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);
 &nbsp;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;

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;
　　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。
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