Cannot get `flash` working in template #2240

fluca1978 · 2025-04-07T15:18:45Z

fluca1978
Apr 7, 2025

In my layout template I've:

    <% my $messages = flash( 'messages' ) || stash( 'messages' ); %>
    <% if ( $messages ) { %>
    <%   for my $msg ( $messages->@* ) { %>
    <div class="alert <%= $msg->{ class } %>" role="alert">
      <div class="d-flex gap-4">
	<span><i class="fa-solid <%= $msg->{ icon } %>"></i></span>
	<div class="d-flex flex-column gap-2">
	  <h6 class="mb-0">
	    <%= $msg->{ title } // '' %>
	  </h6>
	  <p class="mb-0">
	    <%= $msg->{ content } // '' %>
	  </p>

	</div>
      </div>
    </div>
    <%   } %>
    <% }   %>

and in my controller I do something like the following:

sub delete( $self ) {
     ... 
    push $self->stash->{ messages }->@*, "a flash message here";
    $self->redirect_to( q/manifest_list/ );
}

However, while this approach is working for stash (i.e., not redirecting), it is not working on redirect_to where flash should be used.
I've inspected the $self->stash->{ messages } with Data::Dumper and the content is correct, so is something not working on the template/layout side.
What am I missing?

guest20 · 2025-04-07T21:30:05Z

guest20
Apr 7, 2025

You need to use flash before the redirect, not stash

4 replies

guest20 Apr 7, 2025

Also, you're treating your message as an array of regular old strings in delete but the template wants it to be an array of hashes

fluca1978 Apr 8, 2025
Author

Also, you're treating your message as an array of regular old strings in delete but the template wants it to be an array of hashes

Sorry, my fault, something went wrong with copy and paste and I didn't realize. The code looks like the following:

sub delete( $self ) {
     ... 
    push $self->flash->{ messages }->@*, 
                 { content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ };

   # use Data::Dumper;
  # print Dumper( $self->flash->{ messages } );    # shows the right content set before
    $self->redirect_to( q/manifest_list/ );
}

so I am using flash and the hash reference, however, nothing is displayed.

daleif Apr 8, 2025

What does manifest_list do? If that does a redirect as well, then AFAIK the flash msg is lost.

guest20 Apr 8, 2025

@fluca1978 I often get lost in the sauce while exploring a mojo feature I haven't used in the past. Usually what I do is start a new lite app and try to use only that feature in the new app (since one must produce a reproduction case to report a bug).

Usually the process of making the minimal reproduction case shows me the thing I'm doing wrong‡.

In this case you'd want an action that just sets a thing in flash and redirects to a page that dumps the stash / flash / session so you can look directly at it.

__
‡. And if it doesn't show me, it shows the people reading my issue what I'm doing wrong ;)

s1037989 · 2025-04-07T21:30:13Z

s1037989
Apr 7, 2025

I don't see you setting your flash anywhere...

sub delete( $self ) {
     ... 
    push $self->stash->{ messages }->@*, "a flash message here";
    $self->flash(messages => $self->stash->messages)->redirect_to( q/manifest_list/ );
}

0 replies

s1037989 · 2025-04-07T21:32:57Z

s1037989
Apr 7, 2025

flash sets data in the cookie session; stash sets the data in the Mojolicious app controller in-memory stash.

0 replies

fluca1978 · 2025-04-09T07:22:45Z

fluca1978
Apr 9, 2025
Author

Follwing the suggestion of @guest20 the following is a lite-app that does not work as I would expect: calling a GET of /flash redirects to the other page but the flash content is not shown at all.

#!/usr/bin/env perl
use Mojolicious::Lite -signatures;

get '/' => sub ($c) {
  $c->render(template => 'index');
};


get '/manifest_list' => sub ( $c ) {
    $c->render;
};


get '/flash' => sub ( $self ) {
    push $self->flash->{ messages }->@*,
                 { content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ };

    use Data::Dumper;
    print Dumper( $self->flash->{ messages } );    # shows the right content set before
    $self->redirect_to( q/manifest_list/ );
};

app->start;
__DATA__

@@ index.html.ep
% layout 'default';
% title 'Welcome';
<h1>Welcome to the Mojolicious real-time web framework!</h1>


@@ manifest_list.html.ep
% layout 'default';
% title 'LIST';
<h1>LIST</h1>



@@ layouts/default.html.ep
<!DOCTYPE html>
<html>
  <head><title><%= title %></title></head>
	<body>
	<%= content %>
	<%= flash( 'messages' ); %>
    <% my $messages = flash( 'messages' ); %>
    <% if ( $messages ) { %>
				      <h2><%= $messages %></h2>
    <%   for my $msg ( $messages->@* ) { %>
    <div class="alert <%= $msg->{ class } %>" role="alert">
      <div class="d-flex gap-4">
	<span><i class="fa-solid <%= $msg->{ icon } %>"></i></span>
	<div class="d-flex flex-column gap-2">
	  <h6 class="mb-0">
	    <%= $msg->{ title } // '' %>
	  </h6>
	  <p class="mb-0">
	    <%= $msg->{ content } // '' %>
	  </p>

	</div>
      </div>
    </div>
    <%   } %>
    <% }   %>


	</body>
</html>

In the console, before the redirect, the Dumper shows correctly:

$VAR1 = [
          {
            'class' => 'alert-success',
            'title' => 'OK',
            'icon' => 'fa-check',
            'content' => 'a flash message'
          }
        ];

what am I missing here?

0 replies

fluca1978 · 2025-04-09T07:54:39Z

fluca1978
Apr 9, 2025
Author

I found that when the action is called after the redirect, the flash has been cleaned:

get '/manifest_list' => sub ( $self ) {
    use Data::Dumper;
    print Dumper( $self->flash->{ messages } );    # shows nothing

    $self->render;
};

Since the flash is cleaned before render is called, the page is showing nothing. But I don't get why flash does not contain anything after the redirect_to.

3 replies

daleif Apr 9, 2025

Flash sits in cookies, does get /flash from the cli support cookies?

daleif Apr 9, 2025

Also you're running flash('messages') twice.

daleif Apr 9, 2025

This reacts correctly when using morbo file.pl and a browser on port 3000

I'm not entirely familiar with the syntax you're using to add the message to flash, plus you were running flash twice in the template, not sure if that was a problem or not

#!/usr/bin/env perl
use Mojolicious::Lite -signatures;

get '/' => sub ($c) {
  $c->render(template => 'index');
};


get '/manifest_list' => sub ( $c ) {
    $c->render;
};


get '/flash' => sub ( $self ) {
#    push $self->flash->{ messages }->@*,
    #                 { content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ };

    my $a = [{ content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ }];
    $self->flash({ messages => $a});
    $self->redirect_to( q/manifest_list/ );
};

app->start;
__DATA__

@@ index.html.ep
% layout 'default';
% title 'Welcome';
<h1>Welcome to the Mojolicious real-time web framework!</h1>


@@ manifest_list.html.ep
% layout 'default';
% title 'LIST';
<h1>LIST</h1>
    <a href="/flash">Flash</a>
   


@@ layouts/default.html.ep
<!DOCTYPE html>
<html>
  <head><title><%= title %></title></head>
	<body>
	<%= content %>
    <% my $messages = flash( 'messages' ); %>
    % warn dumper $messages;
    % if ( $messages ) {
    there are msg
    % }  
	</body>
</html>

fluca1978 · 2025-04-09T16:17:11Z

fluca1978
Apr 9, 2025
Author

For some reasons I don't understand, this is not working:

get '/flash' => sub ( $self ) {
     push $self->flash->{ messages }->@*,
                  { content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ };
    $self->redirect_to( q/manifest_list/ );
};

while this is working:

get '/flash' => sub ( $self ) {
    $self->flash( messages => [ { content => "a flash message", icon => q/fa-check/, title => 'OK', class => q/alert-success/ } ] );
    $self->redirect_to( q/manifest_list/ );
};

So I guess it is not possible to use flash as an hashref directly.

6 replies

guest20 Apr 10, 2025

There's magic part in the ::Sessions that juggles new_flash and flash in the session when you load the session from the cookie

The "from the previous request" half pulls stuff out of the session and hands it to you when you call flash with one argument

The "stuff from this request" half puts the data from this request into the session in new_stash which is then renamed to flash in the session when the session saved into the cookie so it's there when the previous part looks next request.

When you call flash with a single argument you get the stuff from the previous request, so when you shove stuff in there it's just lost at the end of this request (because the magic doesn't preserve $session->{flash}, it replaces it with new_flash)

What this means is that unlike with session / stash where you can get away with fetching the whole hash and jamming stuff into it, with flash you have to obey the flash('key') and flash(key => new_value) pattern documented for the sub

s1037989 Apr 10, 2025

I've been bitten by this before. I've learned long ago that the Mojolicious documentation is perfectly precise. I think it would be awesome to state this general motto outright at the beginning of the documentation to help remind people of exactly this. It's a warning to read the documentation carefully. More often than not, when I struggle with a Mojolicious function it's because I'm not reading carefully enough. 99/10 when I read the documentation extremely carefully and digest what it says letter for letter, it finally hits me what I'm doing wrong. When I remind myself that Mojolicious documentation is perfectly precise, I find that I get to a solution more quickly soon after.

guest20 Apr 10, 2025

I don't think writing "RTFM" in a manual is going to convince people to read the manual more carefully

fluca1978 Apr 14, 2025
Author

What this means is that unlike with session / stash where you can get away with fetching the whole hash and jamming stuff into it, with flash you have to obey the flash('key') and flash(key => new_value) pattern documented for the sub

This is shockingly complete explanation, thank you very much for the details @guest20 !

guest20 Apr 14, 2025

@fluca1978 I could never figure out how flash worked myself, so this seemed like a good cue to find out.

Also, nice profile pic.

Cannot get flash working in template #2240

Uh oh!

Replies: 6 comments · 13 replies

Uh oh!

Uh oh!

Uh oh!

fluca1978 Apr 8, 2025 Author

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

fluca1978 Apr 9, 2025 Author

Uh oh!

fluca1978 Apr 9, 2025 Author

Uh oh!

Uh oh!

Uh oh!

Uh oh!

fluca1978 Apr 9, 2025 Author

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

fluca1978 Apr 14, 2025 Author

Uh oh!

Cannot get `flash` working in template #2240

Replies: 6 comments 13 replies

fluca1978 Apr 8, 2025
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fluca1978
Apr 9, 2025
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fluca1978
Apr 9, 2025
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fluca1978
Apr 9, 2025
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fluca1978 Apr 14, 2025
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