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Success (Flash) Messages

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Our form submits and saves! But... it's not all that obvious that it works... because we redirect to the homepage... and there's not even a success message to tell us it worked! We can do better!

In ArticleAdminController, give the list endpoint route a name="admin_article_list". After a successful submit, we can redirect there. That makes more sense.

67 lines | src/Controller/ArticleAdminController.php
// ... lines 1 - 14
class ArticleAdminController extends AbstractController
// ... lines 17 - 54
* @Route("/admin/article", name="admin_article_list")
public function list(ArticleRepository $articleRepo)
// ... lines 59 - 65

Adding a Flash Message

With that done, I next want to add a "success" message. Like, after I submit, there's a giant, happy-looking green bar on top that says "Article created! You're a modern-day Shakespeare!".

And... great news! Symfony has a feature that's made for this. It's called a flash message. Oooooo. After a successful form submit, say $this->addFlash(). Pass this the key success - we'll talk about that in a moment - and then an inspirational message!

Article Created! Knowledge is power

67 lines | src/Controller/ArticleAdminController.php
// ... lines 1 - 20
public function new(EntityManagerInterface $em, Request $request)
// ... lines 23 - 25
if ($form->isSubmitted() && $form->isValid()) {
// ... lines 27 - 35
$this->addFlash('success', 'Article Created! Knowledge is power!');
// ... lines 37 - 38
// ... lines 40 - 43
// ... lines 45 - 67

That's all we need in the controller. The addFlash() method is a shortcut to set a message in the session. But, flash messages are special: they only live in the session until they are read for the first time. As soon as we read a flash message, poof! In a... flash, it disappears. It's the perfect place to store temporary messages.

Rendering the Flash Message

Oh, and the success key? I just made that up. That's sort of a "category" or "type", and we'll use it to read the message and render it. And... where should we read and render the message? The best place is in your base.html.twig layout. Why? Because no matter what page you redirect to after a form submit, your flash message will then be rendered.

Scroll down a little bit and find the block body. Right before this - so that it's not overridden by our child templates, add {% for message in app.flashes() %} and pass this our type: success. Remember: Symfony adds one global variable to Twig called app, which comes in handy here.

Inside the for, add a div with class="alert alert-success" and, inside, print message.

92 lines | templates/base.html.twig
// ... lines 1 - 15
// ... lines 17 - 66
{% for message in app.flashes('success') %}
<div class="alert alert-success">
{{ message }}
{% endfor %}
// ... lines 72 - 89
// ... lines 91 - 92

Done! Oh, but, why do we need a for loop here to read the message? Well, it's not too common, but you can technically put as many messages onto your success flash type as you want. So, in theory, there could be 5 success messages that we need to read and print... but you'll usually have just one.

Anyways, let's try this crazy thang! Move back so we can create another important article:

Ursa Minor: Major Construction Planned

Hit enter and... hello nice message! I don't like that weird margin issue - but we'll fix that in a minute. When you refresh, yep! The message disappears in a flash... because it was removed from the session when we read it the first time.

Peeking at the Flash Messages

Ok, let's fix that ugly margin issue... it's actually interesting. Inspect element on the page and find the navbar. Ah, it has some bottom margin thanks to this mb-5 class. Hmm. To make this look right, we don't want to render that mb-5 class when there is a flash message. How can we do that?

Back in base.html.twig, scroll up a bit to find the navbar. Ok: we could count the number of success flash messages, and if there are more than 0, do not print the mb-5 class. That's pretty simple, except for one huge problem! If we read the flash messages here to count them, that would also remove them! Our loop below would never do anything!

How can we work around that? By peeking at the flash messages. Copy the class. Then, say app.session.flashbag.peek('success'). Pipe that to the length filter and if this is greater than zero, print nothing. Otherwise, print the mb-5 class.

93 lines | templates/base.html.twig
// ... lines 1 - 23
<nav class="navbar navbar-expand-lg navbar-dark navbar-bg {{ app.session.flashbag.peek('success')|length > 0 ? '' : 'mb-5' }}">
// ... lines 25 - 93

This... deserves some explanation. First, the global app variable is actually an object called, conveniently, AppVariable! Press Shift+Shift and search for this so we can see exactly what it looks like.

Before, we used the getFlashes() method, which handles all the details of working with the Session object. But, if we need to "peek", we need to work with the Session directly via the getSession() shortcut. It turns out, the "flash messages" are stored on a sub-object called the "flash bag". This new longer code fetches the Session, gets that "FlashBag" and calls peek() on it.

Ok, let's see if that fixed things! Move back over and click to author another amazing article:

Mars: God of War? Or Misunderstood?

Hit enter to submit and... got it! Flash message and no extra margin.

Next, let's learn how we can do... less work! By bossing around the form system and forcing it to create and populate our Article object so we don't have to.