从数据库中的取得image字段的数据,可以保存为指定文件,但为什么文件的大小为0字节?

Question

with w_main.adoquery_ZXSJ do
    begin
      close;sql.Clear;
      sql.Add('select * from ZXSJ');
      open;
      myfilename := ExtractFilePath(Application.ExeName) + fieldbyname('appname_zxsj').AsString;//获得文件的完整路径
//              TBlobField(FieldByName('filestream_ZXSJ')).SaveToFile(fieldbyname('appname_zxsj').AsString);
      myfileStream := TFileStream.Create(myfilename, fmCreate);
      showmessage(myfilename);
      try  //SaveToStream(Stream);
        exeBlobStream := ADOQuery_ZXSJ.CreateBlobStream(FieldByName('filestream_ZXSJ'), bmRead);
        Count := 0;
        try
          if Count = 0 then
          begin
            exeBlobStream.Position := 0;
            Count := exeBlobStream.Size;//showmessage(inttostr(count));
          end;
          Result1 := Count;
          if Count > MaxBufSize then BufSize := MaxBufSize else BufSize := Count;
          GetMem(Buffer, BufSize);
          try
            while Count <> 0 do
            begin
              if Count > BufSize then N := BufSize else N := Count;
              exeBlobStream.ReadBuffer(Buffer^, N);
              exeBlobStream.WriteBuffer(Buffer^, N);
              Dec(Count, N);
            end;
          finally
            FreeMem(Buffer, BufSize);
          end;
        finally
          exeBlobStream.Free;
        end;
      finally
        myfileStream.Free;
      end;
  end;

Answer 1

'select * from ZXSJ'
是取不到图的。

Answer 2

with adoquery_ZXSJ do
            begin
              close;sql.Clear;
              sql.Add('select * from ZXSJ');
              open;
              TBlobField(FieldByName('filestream_ZXSJ')).SaveToFile(fieldbyname('appname_zxsj').AsString);              myini.WriteString('system','version',g_version_sql);//将新版本号写入ini              MessageBox(Handle,pchar('软件升级完成!'),'信息',MB_ICONINFORMATION);
              winexec(pchar(ExtractFilePath(Application.ExeName)+i_exename),SW_SHOWNORMAL);
              application.ShowMainForm:=false;
              application.Terminate;
            end;
但这样是可以的,只是把savetofile函数改成了他里面的具体代码而已??????????????

Answer 3

自己搞定            while Count <> 0 do
            begin
              if Count > BufSize then N := BufSize else N := Count;
              exeBlobStream.ReadBuffer(Buffer^, N);
              exeBlobStream.WriteBuffer(Buffer^, N);//这里错了
              Dec(Count, N);
            end;    exeBlobStream.WriteBuffer(Buffer^, N);//这里错了
改成MyFileBlobStream.WriteBuffer(Buffer^, N);就可以了