Delphi FireDac subsequent parameterized MySQL StoredProcedure execution fails with "Lost connection to MySQL server during query" exception

Question

For a reproduction of the issue, let's have the following two super simple SPs, the first without any parameters, the second with only an output parameter:

1. testsp_0_nopar:
CREATE DEFINER=`root`@`%` PROCEDURE `testsp_0_nopar`()
BEGIN
    #do nothing
END

2. testsp_1_outpar:
CREATE DEFINER=`root`@`%` PROCEDURE `testsp_1_outpar`(OUT result INT)
BEGIN
    SET result=100;
END

If we call the first SP two times, right after each other, then it works without any problem:

var
  sp: TFDStoredProc;
begin
  try
    con.ResourceOptions.AutoReconnect := false; // <- this is important in our project
    con.Connected := True;
    sp := TFDStoredProc.Create(nil);
    try
      sp.Connection := con;
      sp.StoredProcName := 'mydatabase.testsp_0_nopar';
      sp.ExecProc;
      sp.Close;
      sp.ExecProc;
    finally
      sp.Free;
    end;
  except
    on e: exception do
    begin
      ShowMessage(e.Message);
    end;
  end;

But if we call the second SP two times, right after each other, then we get an exception:

var
  sp: TFDStoredProc;
begin
  try
    con.ResourceOptions.AutoReconnect := false; // this is important in our project
    con.Connected := True;
    sp := TFDStoredProc.Create(nil);
    try
      sp.Connection := con;
      sp.StoredProcName := 'mydatabase.testsp_1_outpar';
      sp.Params.Add('result', ftInteger, 1, ptOutput);
      sp.ExecProc;
      sp.Close;
      sp.ExecProc; // <- this second sp call raises an exception
    finally
      sp.Free;
    end;
  except
    on e: exception do
    begin
      ShowMessage(e.Message); // <- Lost connection to MySQL server during query
    end;
  end;

In the real life scenario we have to call the same SP frequently with different parameter values in our project, so it is not a good solution to free-then-recreate the SP object each time.

This worked fine in older Delphi versions using AnyDac, but with FireDac we have this problem.

Thank you very much for any help: :)

Answer 1

It looks like someone also ran into this problem, and posted the solution to Embarcadero's Quality Central: https://quality.embarcadero.com/browse/RSP-31692

So this is a FireDac bug, and to fix it, you have to edit FireDac's source the way the above link instructs you. I can confirm that it solves the problem.