如何使用 ADT 表重试 Delphi TAdsConnection

Question

据我所知，我的会员软件在 FormCreate 过程中使用以下代码连接到多个表：

 {Open the Sessions}
  Membership.LoginPrompt := False;
  Membership.Username := 'ONLINE';
  Membership.Password := '#######';
  Membership.ConnectPath := MembershipLocation;
  Membership.IsConnected := True;
  PosConnection.ConnectPath := PosLocation;
  PosConnection.IsConnected := True;
  Bookings.ConnectPath := BookingsLocation;
  Bookings.IsConnected := True;
  Local.ConnectPath := LocalLocation;
  Local.IsConnected := True;

  // Open all the tables
  for Wk1 := 0 to ComponentCount - 1 do
    begin
    {Skip the Tmp / New Tables}
    if ((Components[Wk1] is TAdsTable) and (TAdsTable(Components[Wk1]).Name = 'NewTable')) then
      Continue;
    if ((Components[Wk1] is TAdsTable) and (TAdsTable(Components[Wk1]).Name = 'TmpTable')) then
      Continue;
    {Is it a TTable}
    if Components[Wk1] is TAdsTable then
      TAdsTable(Components[Wk1]).Active := True;
    {Is it a TwwTable}
    if Components[Wk1] is TwwTable then
      TwwTable(Components[Wk1]).Active := True;
    {Is it a TQuery}
    if Components[Wk1] is TAdsQuery then
      TAdsQuery(Components[Wk1]).Active := True;
    end;


  {Activate the Membership Tables. This is due to passwords}
  Members.Active := True;
  MemTypes.Active := True;
  MembersById.Active := True;
  MemBookMSys.Active := True;

  {Rebuild the Secondry index on the MemBook table}
  if RebuildIdx = True then
    begin
    MemBook.Active := False;
    MemBook.Exclusive := True;
    MemBook.Active := True;
//  Check(DbiRegenIndexes(MemBook.Handle));
    MemBook.Active := False;
    MemBook.Exclusive := False;
    MemBook.Active := True;
    end;
  {Make the Table Active}
  MemBook.Active := True;

有时，当服务器尚未准备好时，连接会失败并且用户收到 Advantage 错误 7.xxx

我需要它重试连接多次，或者在经过一定时间后再次连接。

对于这种情况，是否有一种标准的错误捕获和重试连接方法？或者我应该在一段时间过去后重复该代码？

谢谢

Answer 1

您可以使用标准 try.. except 处理。

function TYourDataModule.ConnectToDatabases: Boolean;
begin
  Result := False;

  Membership.LoginPrompt := False;
  Membership.Username := 'ONLINE';
  Membership.Password := '#######';
  Membership.ConnectPath := MembershipLocation;
  PosConnection.ConnectPath := PosLocation;
  Bookings.ConnectPath := BookingsLocation;
  Local.ConnectPath := LocalLocation;

  // Try to make all the connections together. If any fail, we'll
  // hit the except block.
  try
    Membership.IsConnected := True;
    PosConnection.IsConnected := True;
    Bookings.IsConnected := True;
    Local.IsConnected := True;
  except
    on E: EAdsDatabaseError do
    begin
      // Make sure all connections are closed, in case
      // one or more succeeded before a failure. We'll
      // be set for next time.
      Membership.IsConnected := False;
      PostConnection.IsConnected := False;
      Booking.IsConnected := False;
      Local.IsConnected := False;
      Result := False;
    end;
  end;
end;

然后，您的调用代码可以在循环中使用该函数，直到它返回 true 或超过尝试次数：

var
  NumTrys: Integer;
const
  MAX_TRYS = 10;
  TRY_DELAY = 1000;
begin
  NumTrys := 0;
  while NumTrys < MAX_TRYS do
  begin
    if YourDataModule.ConnectToDatabases then
      Break;
    Inc(NumTrys);
    Sleep(TRY_DELAY);
  end;
  if NumTrys = MAX_TRYS then
    // Handle not being able to connect after all attempts.
end;

请注意，在 IDE 中运行时您将看到有关连接失败的异常消息，但在运行时则不会。如果您不想在 IDE 中看到它们，可以在“项目选项”对话框中关闭对 EADSDatabaseError 的处理。