Tadoblobstream.Create出错？请帮忙解释一下

Question

procedure Tfrmretailupdate.Button1Click(Sender: TObject);
var filename:string;
  bs:Tadoblobstream;
begin
  with adoquery1 do begin
    close;
    sql.Clear;
    sql.Add('select f_name,f_program from T_retailversionupdate where f_name='''+'retail.exe'+'''');
    open;
    filename:=adoquery1.fieldbyname('f_name').AsString;
    showmessage('test');
    bs:=Tadoblobstream.Create(Tblobfield(adoquery1.FieldByName('f_name')),bmRead);
    bs.SaveToFile(filename);
    bs.Free;
  end;
end;执行到这一步bs:=Tadoblobstream.Create(Tblobfield(adoquery1.FieldByName('f_name')),bmRead);出错，提示‘invalid variant type’ 是什么意思？

Answer 1

历史一般性是:TBlobField(A_ADO_Field).SaveToStream(ms); //MS: TMemoryStream
ms.SaveToFile(....);