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09.

Fetching Data & The Repository

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Our question table has data! And each time we refresh, we got more data! You get a question! You get a question!

Copy the slug from the latest one and then go to /questions/that-slug to see it. Except... this is not actually that question. The name is kinda right... but that's it. Over in the show() action, this is because nothing is being loaded from the database. Lame!

Here's our next mission: use the $slug to query for a row of Question data and use that to make this page truly dynamic. How? The entity manager that we use to save data can also be used to fetch data.

The Repository

Start by adding a third argument: EntityManagerInterface $entityManager. This interface has a bunch of methods on it. But... most of the time, you'll only use three: persist() and flush() to save, and getRepository() when you want to get data.

97 lines | src/Controller/QuestionController.php
// ... lines 1 - 12
class QuestionController extends AbstractController
{
// ... lines 15 - 70
public function show($slug, MarkdownHelper $markdownHelper, EntityManagerInterface $entityManager)
{
// ... lines 73 - 94
}
}

Say $repository = $entityManager->getRepository() and pass the entity class that we want to query. So Question::class.

97 lines | src/Controller/QuestionController.php
// ... lines 1 - 12
class QuestionController extends AbstractController
{
// ... lines 15 - 70
public function show($slug, MarkdownHelper $markdownHelper, EntityManagerInterface $entityManager)
{
if ($this->isDebug) {
$this->logger->info('We are in debug mode!');
}
$repository = $entityManager->getRepository(Question::class);
// ... lines 78 - 94
}
}

Whenever you need to get data, you'll first get the repository for an entity. This repository object is really really good at querying from the question table. And it has several methods to help us.

For example, we want to query WHERE the slug column equals the $slug variable. Do that with $question = $repository-> and... this auto completes a bunch of methods. We want findOneBy(). Pass this an array of the WHERE statements we need: 'slug' => $slug. After, dd($question).

97 lines | src/Controller/QuestionController.php
// ... lines 1 - 12
class QuestionController extends AbstractController
{
// ... lines 15 - 70
public function show($slug, MarkdownHelper $markdownHelper, EntityManagerInterface $entityManager)
{
// ... lines 73 - 76
$repository = $entityManager->getRepository(Question::class);
$question = $repository->findOneBy(['slug' => $slug]);
dd($question);
// ... lines 80 - 94
}
}

Ok, let's see what this returns! Refresh and... woohoo! This gives us a Question object. Doctrine finds the matching row of data and uses that to populate an object, which is beautiful.

The repository has a number of other methods on it. For example, findOneBy() returns a single object and findBy() returns an array of objects that match whatever criteria you pass. The findAll() method returns an array of all Question objects and there are a few others. So without doing any work, we can easily execute the most basic queries. Now, eventually we will need to do more complex stuff - and for that, we'll write custom queries. We'll see that later.

404 On Not Found

So when Doctrine finds a matching row, we get back a Question object. But if we change the slug in the URL to something that does not exist, we get null. So: a Question object or null.

Let's think: what do we want to do when someone goes to a URL that doesn't match a real question? The answer is: trigger a 404 page! Great! Um... how do we trigger a 404 page in Symfony?

First, this is optional - I'm going to say /** space and then type Question|null.

101 lines | src/Controller/QuestionController.php
// ... lines 1 - 12
class QuestionController extends AbstractController
{
// ... lines 15 - 70
public function show($slug, MarkdownHelper $markdownHelper, EntityManagerInterface $entityManager)
{
// ... lines 73 - 77
/** @var Question|null $question */
$question = $repository->findOneBy(['slug' => $slug]);
// ... lines 80 - 98
}
}

This simply helps my editor know that this is a Question object or null, which will assist auto-completion. And, to be honest, PhpStorm is so smart that... I think it already knew this.

Below, if not $question, trigger a 404 page by saying throw $this->createNotFoundException(), which is a method on the parent AbstractController class. Pass this any message you want:

No question found for slug %s

And pass the $slug variable.

101 lines | src/Controller/QuestionController.php
// ... lines 1 - 12
class QuestionController extends AbstractController
{
// ... lines 15 - 70
public function show($slug, MarkdownHelper $markdownHelper, EntityManagerInterface $entityManager)
{
// ... lines 73 - 77
/** @var Question|null $question */
$question = $repository->findOneBy(['slug' => $slug]);
if (!$question) {
throw $this->createNotFoundException(sprintf('no question found for slug "%s"', $slug));
}
// ... lines 83 - 98
}
}

That's it! But notice the throw. createNotFoundException() instantiates an exception object - a very special exception object that triggers a 404 page. Most of the time in Symfony, if you throw an exception, it will cause a 500 page. But this special exception maps to a 404.

Let's try it: refresh and... yes! You can see it up here: "404 Not found" with our message.

Two things about this. First: this is the development error page. If we changed the environment to prod, we would see a much more boring 404 page with no error or stack trace details. We won't talk about it, but the Symfony docs have details about how you can customize the look and feel of your error pages on production.

The second thing I want to say is that the message - no question found for slug - is something that only developers will see. Feel free to make this as descriptive as you want: you don't need to worry about a real user seeing it.

Now that we have a Question object in our controller, let's use it in our template to render real, dynamic info. That's next.