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;
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。
在"DELPHI存取JPEG文件到SQL Server数据库"发表之后，有许多网友来电表示支持和相关的技术咨询，在此首先对那些关心本文的朋友们表示衷心的感谢。
由于网友的需要做一个档案管理系统，存取jpeg文件到sql 2000数据库中，但在dbimage中及qrdbimage中均不能正常显示jpeg的文件，此为borland的限制，虽然使用第三方控件能达到要求，但我们还是来原始的实现一下这方面的技术，其实原理十分简单，既然我们在"DELPHI存取JPEG文件到SQL Server数据库"能存储jpeg文件，也能在image中显示，但一接触db类的图象显示控件就行不通了，我们可以在jpeg文件存入数据库之前转换成bmp文件再存入数据库即可，程序运行环境delphi5+ado+sql 2000桌面版+win98se2最终版，数据库中存放图片字段的类型为image，程序源代码如下：
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
Db, DBCtrls, Grids, DBGrids, ADODB, ExtDlgs,jpeg, ExtCtrls, StdCtrls;
type
TForm1 = class(TForm)
ADOConnection1: TADOConnection;
ADOQuery1: TADOQuery;
DataSource1: TDataSource;
DBGrid1: TDBGrid;
DBImage1: TDBImage;
ADOQuery1ID: TStringField;
ADOQuery1FIELD: TStringField;
ADOQuery1STYLE: TStringField;
ADOQuery1SYSTEM: TStringField;
ADOQuery1DATE: TDateTimeField;
ADOQuery1PERSON1: TStringField;
ADOQuery1PERSON2: TStringField;
ADOQuery1PERSON3: TStringField;
ADOQuery1PHOTO: TBlobField;
ADOQuery1DESCRIPTION: TStringField;
OpenPictureDialog1: TOpenPictureDialog;
Image1: TImage;
Button1: TButton;
Memo1: TMemo;
procedure DBImage1Click(Sender: TObject);
procedure Button1Click(Sender: TObject);
procedure FormShow(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.DBImage1Click(Sender: TObject);
var
picstream:tadoblobstream;
bmppic:tbitmap;
jpgpic:tjpegimage;
bmpstream:TMemoryStream;
begin
if form1.OpenPictureDialog1.Execute then
begin
if extractfileext(form1.openpicturedialog1.filename)='.bmp' then
begin
adoquery1.edit;
picstream:=tadoblobstream.Create(tblobfield(ADOQuery1PHOTO),bmWrite);
//注：上句代码中的ADOQuery1PHOTO是adoquery1中的固定字段photo的固定字段的name
//用户需要手工添加固定字段，也可用fields[i]来进行选择，这点在
//"DELPHI存取JPEG文件到SQL Server数据库"这篇文章中没有注释，至使许多朋友没有
//编译成功。
picstream.LoadFromFile(openpicturedialog1.filename);
picstream.Position:=0;
adoquery1.edit;
tblobfield(ADOQuery1PHOTO).loadfromstream(picstream);
adoquery1.post;
adoquery1.edit;
picstream.free;
end
else
begin
jpgpic:=tjpegimage.Create;
bmppic:=tbitmap.Create;
bmpstream:=tmemorystream.Create;
jpgpic.LoadFromFile(openpicturedialog1.filename);
bmppic.Assign(jpgpic);
bmppic.SaveToStream(bmpstream);
adoquery1.edit;
picstream:=tadoblobstream.Create(tblobfield(ADOQuery1PHOTO),bmWrite);
//注：上句代码中的ADOQuery1PHOTO是adoquery1中的固定字段photo的固定字段的name
//用户需要手工添加固定字段，也可用fields[i]来进行选择，这点在
//"DELPHI存取JPEG文件到SQL Server数据库"这篇文章中没有注释，至使许多朋友没有
//编译成功。
picstream.LoadFromStream(bmpstream);
picstream.Position:=0;
adoquery1.edit;
tblobfield(ADOQuery1PHOTO).loadfromstream(picstream);
adoquery1.post;
jpgpic.free;
bmppic.free;
bmpstream.free;
adoquery1.edit;
picstream.free;
end;
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
memo1.Lines.Add(form1.openpicturedialog1.filter);
end;
procedure TForm1.FormShow(Sender: TObject);
begin
form1.openpicturedialog1.filter:='All *.jpg;*.jpeg;*.bmp;|*.jpg;*.jpeg;*.bmp;)';
end;
end.
至此实现的功能代码如上所例，希望能对需要这方面资料的朋友有所帮助.
