DELPHI中对SQL SERVER中image、text字段的读写综述

下面通过详细的例子来讲述如何在delphi中处理sql server中的image、text字段。因为实际开发的需要， 我们需要处理的是text类型的字段，包括读和写。网上很多相关的文章都是讲述的对image的读写操作，下面首先介绍如何将图象存储在sql server的image字段。
其中 DataMConn为一个针对数据库操作的单元，放置一个ADOConnection,一个ADOQuery

//image to database
procedure TfrmText.Button1Click(Sender: TObject);
var
  bm:tbitmap;
  ms:TMemoryStream;
begin
  ms:=TMemoryStream.Create;      

  bm:=TBitmap.Create;
  bm.Assign(image1.Picture.Bitmap);
  bm.SaveToStream(ms);
  with DataMConn.ADOQHistory do
    begin
      Close;
      SQL.Clear;
      SQL.Add('INSERT INTO Package(PackageID,TempPackage) VALUES(:x,:y)');
      Parameters.ParamByName('y').LoadFromStream(ms,ftBlob);
      Parameters.ParamByName('x').Value   :=  'aaaaa';
      ExecSQL;
   end;
end;

//show image
procedure TfrmText.Button2Click(Sender: TObject);
var
    Stream:TStream;
    bm:tbitmap;
begin
      with DataMConn.ADOQHistory do
        begin
          Close;
          SQL.Clear;
          SQL.Add('SELECT * FROM Package WHERE packageID= ''aaaaa''');
          Try
            Open;
            stream := DataMConn.ADOQHistory.CreateBlobStream(FieldByName('TempPackage'),bmRead);
            bm:=TBitmap.Create;
            bm.LoadFromStream(stream);
            image2.Picture.bitmap.Assign(bm);
            stream.Free;
          except
            begin
              ShowMessage('Error!');
              Exit;
            end;
          end;//try
        end;
end;

下面的两个例子是如何处理text类型的字段，其中读取的时候，利用了一个TDBMemo控件，来加载读取的流数据，然后赋值给一个WideString类型的变量str
//text to stream
procedure TfrmText.Button3Click(Sender: TObject);
var
  str : WideString;
  ss:TStringStream;
  i : integer;
begin
  str := 'sstrstrststrstrststrstrstrsttrstrstrrstrstr';         
  for i := 1 to 10000 do
    begin
      str := str + 'sstrstrststrstrststrstrstrsttrstrstrrstrstr';    //43万多个字节
    end;
  str := str + 'E';
  ss := TStringStream.Create(str);         
  //bm:=TBitmap.Create;
  //bm.Assign(image1.Picture.Bitmap);
  //bm.SaveToStream(ms);
  with DataMConn.ADOQHistory do
    begin
      Close;
      SQL.Clear;
      SQL.Add('INSERT INTO tPackage(PackageID,TempPackage) VALUES(:x,:y)');
      Parameters.ParamByName('y').LoadFromStream(ss,ftMemo);
      Parameters.ParamByName('x').Value   :=  'aaaaa';
      ExecSQL;
   end;
end;

//read text  to a TDBMemo

procedure TfrmText.Button4Click(Sender: TObject);
var
  stream : TStream;
  str : WideString;
begin
  with DataMConn.ADOQHistory do
   begin
    Close;
    SQL.Clear;
    SQL.Add('SELECT TempPackage FROM tPackage WHERE packageID= ''aaaaa''');
    Open;
    if not IsEmpty then
      begin
        Stream := DataMConn.ADOQHistory.CreateBlobStream(FieldByName('TempPackage'),bmRead);
        stream.Position := 0;
        AMemo.Lines.LoadFromStream(stream);
        stream.Free;
      end;
   end;
end;

//下面是把text字段的数据内容直接读到一个WideString中，而不通过TDBMemo，因为在实际中，不知道何种原因，线程读到数据后，只能在第一次处理时正常，然后再用鼠标点应用程序，程序就停了……who knows the reason , pls tell me & 3ks

procedure TfrmText.Button5Click(Sender: TObject);
var
  Buffer: PChar;
  MemSize: Integer;
  Stream: TStream;
  str : WideString;
begin
  with DataMConn.ADOQHistory do
   begin
    Close;
    SQL.Clear;
    SQL.Add('SELECT TempPackage FROM tPackage WHERE packageID= ''aaaaa''');
    Open;
    if not IsEmpty then
      begin
        Stream := DataMConn.ADOQHistory.CreateBlobStream(FieldByName('TempPackage'),bmRead);
      try
        MemSize := Stream.Size;
        Inc(MemSize);                   //Make room for the buffer's null terminator.
        Buffer := AllocMem(MemSize);     //Allocate the memory.
        try
          Stream.Read(Buffer^, MemSize);  //Read TempPackage field into buffer.
          str := Buffer;
        finally
          FreeMem(Buffer, MemSize);
        end;
      finally
        Stream.Free;
      end;
    end;
   end;
end;