[Dancer-users] Flash Message

[Flavio Poletti]

Hi,

   I thought a bit about it and I think that the current implementation is a
bit too limited (this seems also what brian thinks in the bug report
http://rt.cpan.org/Public/Bug/Display.html?id=65009 - at least from what I
understand).

The problem is that the flash message might have to be displayed in the next
request, which happens when redirections kick in. In this case, the flash
message should be set, kept in the session and removed only when it is
actually displayed; this should happen automatically, i.e. without playing
with the $persistent variable - which is global - or with further overhead
on the controller side.

Following brian's feedback, I tried to re-code the plugin with the following
criteria:

* the "flash" method only adds messages (and handles many of them for every
category - you might have more than one error in a page). I see no point in
removing messages while inside the controller;
* the message removal logic is shifted in the template via an anonymous sub.
If the sub is called then the flash cache is cleared, otherwise it remains
there. This should guarantee that the messages are not removed until they
get the chance to be displayed.

This is the core of the recoding - not tested but should suffice to give you
the idea:

register flash => sub {
    my ($key, $value) = @_;
    my $flash = session($session_hash_key);
    if (! $flash) { # initialise the container for flash messages
      $flash = {};
      session($session_hash_key, $flash);
    }
    push @{$flash->{$key}}, $value;
    return;
};

before_template sub {
   my $obj = shift;
   my $flashes;
   $obj->{$token_name} = sub {
      if (! $flashes) { # first call, get messages and clear
         $flashes = session($session_hash_key) || {};
         session($session_hash_key, {});
      }
      return $flashes;
   };
   return;
};


IMHO there is no need for an "exists", in the template you can do like this:

<% IF flash.errors %>...<% END %>

The important thing to remember is that even checking for the presence of
something inside "flash" clears the messages, which is consistent with the
semantics that "they get cleared as soon as they have a chance to be
displayed". The $flashes variable guarantees that they survive at least
until the end of the request, i.e. you are able to call "flash" multiple
times while handling a request and always get all messages.

If you think that this makes sense, I can propose a pull request on GitHub
or you can make the changes directly.

Cheers,

   Flavio.



On Tue, Jan 11, 2011 at 5:48 PM, damien krotkine <dkrotkine at gmail.com>wrote:

> I've re-implemented it to be more Rails-like, as sukria said.
>
> https://github.com/dams/Dancer-Plugin-FlashMessage
>
> and on CPAN, pending  mirrors refresh.
>
> The funny part of the story ? the effective code is only 30 lines
> long. Talking about Perl and Dancer expressiveness...
>
> dams.
>
> On 11 January 2011 14:40, Alexis Sukrieh <sukria at sukria.net> wrote:
> > Hi list!
> >
> > Le 11/01/2011 14:29, damien krotkine a écrit :
> >>
> >> Hi,
> >>
> >> following previous thread, I've done a first implementation of
> >> Dancer::Plugin::FlashMessage :
> >>
> >> https://github.com/dams/Dancer-Plugin-FlashMessage
> >
> > Great! Thanks a lot for your time dams, the myth is still alived!
> (Dancer's
> > community)++
> >
> >
> >
> >> Some parts need to be improved, for instance :
> >>
> >> - it supports only one flash message
> >> - the keywords are not short enough.
> >>
> >> So I think I'll change the implementation so that the template token is
> >> simply called 'flash', and it'll be a hash, like in Rails. I'll also
> >> change the registered method so that it's just flash() instead of
> >> get_flash()
> >
> > I agree. I'd like to behave just like Rails' flash feature. The idea is
> > pretty straight forward:
> >
> > "flash" is an accessor to a particular session hash table whose values
> can
> > only be accessed once. Nothing more complicated than that.
> >
> > So to conclude, IMO, flash should be a wrapper like the following:
> >
> >    sub flash {
> >        my ($key, $value) = @_;
> >        my $flash = session('_flash');
> >
> >        # write
> >        if (@_ == 2) {
> >             $flash->{$key} = $value;
> >             session('_flash' => $flash);
> >        }
> >
> >        # read (+ delete)
> >        else {
> >            my $value = $flash->{$key};
> >            delete $flash->{$key} if defined $value;
> >            session('_flash' => $flash);
> >        }
> >
> >        return $value;
> >    }
> >
> > This is it, I think. This allows for the following code in a Dancer app:
> >
> >
> >     get '/' => sub {
> >         flash welcome => "This is a welcome message, only shown once";
> >     }
> >
> > Then, as soon as the key 'welcome' is accesed via flash('welcome'), the
> > entry will be purged.
> >
> > This will be very helpful for authentication stuff in before filters,
> error
> > messages, notifications, ....
> >
> >
> > Kudos to dams!
> >
> > (BTW I haven't read the code yet)
> >
> > --
> > Alexis Sukrieh
> > _______________________________________________
> > Dancer-users mailing list
> > Dancer-users at perldancer.org
> > http://www.backup-manager.org/cgi-bin/listinfo/dancer-users
> >
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