Delphi 2007 DBX Access Violation in dbxmys30.dll

I'm trying to use the dbexpress components in Delphi 2007 to connect to a MySQL database but getting an error the reads "Access violation at address 0B86E258 in module 'dbxmys30.dll'. Read of address 00000000".

I have a TSQLConnection using the MySQL drivers and setup to connect to a MySQL 5.1 database. I can set it to active without a problem.

The problem arises when I try to get data from the database using any number of components. To be more specific, I have a TSQLTable object. I set the SQLConnection parameter开发者_开发知识库 to the TSQLConnection I created and set table name to a table in my database. When I try to set Active to true I get the error. This happens in design mode as well as at runtime. It will also happen with any other dbx component that try to get data from the database.

I'm running Windows 7 64 bit with a MySQL 5.1 client and server. I can run queries on the database using MySQL Query Browser without any issues.

Any Help would be much appreciated. Thanks!

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You have a version incompatibility, the version of 'libmysql.dll' you're using is incompatible with the version that the dbx driver is built against. This thread on embarcadero forums suggests to use version '5.0.27' and this thread suggests '5.0.24'. The latest version I had success was '5.1.11'.

BTW, because 'libmysql.dll' contains no version info, I was fed up with keeping track of which dll was which version and I had to wrote this little thing:

type
  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FLastFile: string;
    procedure WMDropFiles(var Msg: TWMDropFiles); message WM_DROPFILES;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

uses
  shellapi;

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  DragAcceptFiles(Handle, True);
  Width := 350;
  Height := 110;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  DragAcceptFiles(Handle, False);
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  R: TRect;
begin
  Canvas.TextOut(40, 16, 'Drop libmysql.dll to find out version');
  R := Rect(14, 40, ClientWidth, ClientHeight);
  DrawText(Canvas.Handle, PChar(FLastFile), Length(FLastFile), R, DT_LEFT);
end;

function GetVersion(ClientDll: PChar): UINT;
const
  FUNC          = 'mysql_get_client_version';
  FUNCTIONNOTFOUND = '%s: ''%s'' in ''%s''.';
  UNABLETOLOADLIB  = 'Unable to load library (''%s''): ''%s''.';
var
  LibHandle: HMODULE;
  GetClientVersionFunc: function: Integer;
begin
  Result := 0;
  LibHandle := LoadLibrary(ClientDll);
  if LibHandle <> 0 then begin
    try
      @GetClientVersionFunc := GetProcAddress(LibHandle, FUNC);
      if @GetClientVersionFunc <> nil then begin
        Result := GetClientVersionFunc;
      end else
        raise EOSError.CreateFmt(FUNCTIONNOTFOUND,
            [SysErrorMessage(GetLastError), FUNC, ClientDll]);
    finally
      FreeLibrary(LibHandle);
    end;
  end else
    raise EOSError.CreateFmt(UNABLETOLOADLIB, [ClientDll,
        SysErrorMessage(GetLastError)]);
end;

procedure TForm1.WMDropFiles(var Msg: TWMDropFiles);
var
  len: Integer;
  DropName: string;
  Ver: UINT;
begin
  len := DragQueryFile(Msg.Drop, 0, nil, 0) + 1;
  SetLength(DropName, len);
  len := DragQueryFile(Msg.Drop, 0, PChar(DropName), len);
  SetLength(DropName, len);
  try
    try
      Ver := GetVersion(PChar(DropName));
    except
      FLastFile := '';
      raise;
    end;
    if Boolean(Ver) then
      FLastFile := DropName + #10 +'[' + IntToStr(Ver) + ']  -  ' +
          IntToStr(Ver div 10000) + '.' + IntToStr((Ver div 100) mod 100)
          + '.' + IntToStr(Ver mod 100)
    else
      FLastFile := '';
  finally
    Invalidate;
    DragFinish(Msg.Drop);
    Msg.Result := 0;
  end;
end;

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Access Violation ... read of address 00000000 means that something is trying to dereference a nil pointer. Do you have the source to dbxmys30.dll? If so, this will be very easy to debug. If not, there's not much you can do except file a bug report (who created dbxmys30.dll, BTW?) and hope it gets fixed quickly.