How to solve a closed dataset error when running an update query in Delphi 7?

问题

I keep getting an error in Delphi 7 with my application that uses the Microsoft Jet engine and a Microsoft Access (*.mdb) database. I am making the connection via a TADOQuery component. The error says 'Cannot perform this operation on a closed dataset' and happens only in one event handler when trying to execute an UPDATE query:

frmHome.adoqryMain.SQL.Text := 'UPDATE Predictions SET Complete = True WHERE UID = "'+sUID+'"';

The event handler's code is as follows:

    procedure TfrmAdmin.bmbSubmitClick(Sender: TObject);
var
  sScore, sEID, sPrediction, sUID : String;
  iRecordCount, x, iPos, iLength, iActual, iPoints, iPointsNew : Integer;
  rPrediction : Real;
begin
  // Assign values to variables
  sScore := IntToStr(sedSuthies.Value) + '-' + IntToStr(sedOpponent.Value);
  iActual := sedSuthies.Value + sedOpponent.Value;
  sEID := frmHome.arrEID[lstEvents.ItemIndex];
  // Update the score for the event in the database
  frmHome.adoqryMain.Active := False;
  frmHome.adoqryMain.SQL.Clear;
  frmHome.adoqryMain.SQL.Text := 'UPDATE Events SET Score = "'+sScore+'",Complete = True WHERE EID = "'+sEID+'" ';
  frmHome.adoqryMain.ExecSQL;
  frmHome.adoqryMain.SQL.Text := 'SELECT * FROM Predictions WHERE EID = "'+sEID+'" ';
  frmHome.adoqryMain.Open;
  iRecordCount := frmHome.adoqryMain.RecordCount;
  //Assign points to users for all the predictions
  for x := 0 to (iRecordCount - 1) do begin
    sUID := frmHome.adoqryMain.Fields[1].AsString;
    sPrediction := frmHome.adoqryMain.Fields[4].AsString;
    iPos := Pos('-',sPrediction) - 1;
    iLength := Length(sPrediction) - iPos;
    ShowMessage('1');
    if ((sedSuthies.Value >= sedOpponent.Value) AND (StrToFloat(Copy(sPrediction, 1, iPos)) >= StrToFloat(Copy(sPrediction, iPos + 2, iLength + 1)))) OR ((sedSuthies.Value < sedOpponent.Value) AND (StrToFloat(Copy(sPrediction, 1, iPos)) < StrToFloat(Copy(sPrediction, iPos + 2, iLength + 1)))) then begin
      rPrediction := StrToFloat(Copy(sPrediction, iPos + 2, iLength + 1)) + StrToFloat(Copy(sPrediction, 1, iPos));
      if rPrediction >= iActual then
        rPrediction := rPrediction - iActual
      else
        rPrediction := iActual - rPrediction;
      iPoints := Round(10 * (1 - (rPrediction / iActual)));
    end
    else
      iPoints := 0;
    ShowMessage('2');
    frmHome.adoqryMain.Open;
    frmHome.adoqryMain.SQL.Text := 'UPDATE Predictions SET Complete = True WHERE UID = "'+sUID+'"';
    frmHome.adoqryMain.ExecSQL;
    ShowMessage('3');
    ShowMessage(IntToStr(iPoints));
    frmHome.adoqryMain.Next;
  end;
  ShowMessage('Score succefully submitted!');
  frmHome.UpdateEventLists;
end;

It's a bit messy at the moment, but irrespective of what the UPDATE query updates, it always gives this error. I've tried opening the TADOQuery, using various methods of running the query (with statement and parameters), etc. Any help would be greatly appreciated.

P.S. The ShowMessage functions are there for debugging purposes and will be removed.

回答1:

I think I see what you're trying to do. You're using the same qry both to fetch data from, and in the loop you use it to update the database.

Start using 2 adoqueries and then it should work.

So Adoquerymain, and a new AdoQueryInLoop

ShowMessage('2');
frmHome.adoqryInLoop.Close; //I'm an overzealous query closer
frmHome.adoqryInLoop.SQL.Text := 'UPDATE Predictions SET Complete = True WHERE UID = "'+sUID+'"';
frmHome.adoqryInLoop.ExecSQL;
ShowMessage('3');

来源：https://stackoverflow.com/questions/19763899/how-to-solve-a-closed-dataset-error-when-running-an-update-query-in-delphi-7