Delphi - 使用 ZLib 壓縮 TStringList 並保存到 SQL VARBINARY 列

Question

我需要從 TStringList 中獲取值，使用 System.ZLIb 庫對其進行壓縮，並將其作為 VARBINARY(MAX) 列保存到 SQL 服務器數據庫中。

到目前為止，我已經能夠從 SQL 表中讀取壓縮數據，將其解壓縮並將其加載到 TStringList 中。 但是，將數據保存回數據庫是我的問題所在，我無法讓它工作。 根據 Embarcadero docwiki，這應該是一個非常簡單的過程： http://docwiki.embarcadero.com/CodeExamples/Sydney/en/ZLibCompressDecompress_(Delphi)

這是更新我的 SQL 表的代碼。 當我到達“CompressedStrm.CopyFrom(InputStream, InputStream.Size);” 行，我收到“流讀取錯誤”錯誤。

procedure TdmMain.SaveSystemSetting(SettingName: string; Settings: TStringList);
var
  InputStream, OutputStream: TMemoryStream;
  CompressedStrm: TCompressionStream;
begin
  InputStream:= TMemoryStream.Create;
  OutputStream:= TMemoryStream.Create;
  try
    Settings.SaveToStream(InputStream, TEncoding.Default);

    CompressedStrm := TCompressionStream.Create(clDefault, OutputStream);
    try
      CompressedStrm.CopyFrom(InputStream, InputStream.Size);
      OutputStream.SaveToFile('c:\output.zip');
    finally
      FreeAndNil(CompressedStrm);
    end;

    {save settings to the database}
    qryWork.Close;
    qryWork.SQL.Clear;
    qryWork.SQL.Add('UPDATE SystemSettings');
    qryWork.SQL.Add('   SET Setting = :data');
    qryWork.SQL.Add(' WHERE SettingName = ''' + SettingName + '''');
    qryWork.Parameters.ParamByName('data').LoadFromStream(OutputStream, ftBlob);
    qryWork.ExecSQL;
  finally
    FreeAndNil(InputStream);
    FreeAndNil(OutputStream);
  end;
end;

以下代碼從數據庫中讀取，解壓縮數據並加載 TStringList - 它可以 100% 工作：

procedure TdmMain.GetSystemSetting(SettingName: string; var Settings: TStringList);
var
  SettingBlob: TBlobField;
  DecompStream: TDecompressionStream;
  InputStream, OutputStream: TMemoryStream;
begin
  qryWork.Close;
  qryWork.SQL.Clear;
  qryWork.SQL.Add('SELECT Setting');
  qryWork.SQL.Add('  FROM SystemSettings');
  qryWork.SQL.Add(' WHERE SettingName = ''' + SettingName + '''');
  qryWork.Open;
  if not qryWork.EOF then
  begin
    SettingBlob := qryWork.FieldByName('Setting') as TBlobField;

    InputStream := TMemoryStream.Create;
    OutputStream := TMemoryStream.Create;
    try
      SettingBlob.SaveToStream(InputStream);
      InputStream.Position := 0;

      DecompStream := TDecompressionStream.Create(InputStream);
      try
        OutputStream.CopyFrom(DecompStream, 0);
        OutputStream.Position := 0;
        Settings.LoadFromStream(OutputStream, TEncoding.Default);
      finally
        FreeAndNil(DecompStream);
      end;
    finally
      FreeAndNil(InputStream);
      FreeAndNil(OutputStream);
    end;
  end;
  qryWork.Close;
end;

Answer 1

忘記重新定位輸入 stream...

  try
    Settings.SaveToStream(InputStream, TEncoding.Default);
    InputStream.Position := 0;
    ...