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04.

Cache Service and Cache Pools

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Okay, we injected HttpClientInterface and made an HTTP request to fetch some JSON data that we rendered on our website. But executing an HTTP request on every single page load is not a good idea. HTTP requests are slow, and we can already see that happening here, where our homepage loads are taking longer than they were before. And the ISS moves fast, so it's not very efficient to update this information constantly. Is there a service that can cache that data instead? You bet!

Finding the Cache Service

Open your terminal and run

bin/console debug:autowiring cache

to see if we have any cache-related services and... we do! These cache.app aliases are ready to be used in our application. Another thing to note is this CacheItemPoolInterface. Pools are just unique namespaces for cached items. You might think of them as "subfolders" in the global cache directory. That means you can clear one cache pool without affecting the others. We'll talk about that more later.

For now, we're going to keep it simple and use CacheInterface. Back in our code, inside homepage(), write CacheInterface (the one from Contracts) and call it $cache.

40 lines | src/Controller/MainController.php
// ... lines 1 - 9
use Symfony\Contracts\Cache\CacheInterface;
// ... lines 11 - 13
class MainController extends AbstractController
{
// ... line 16
public function homepage(
// ... lines 18 - 19
CacheInterface $cache,
): Response {
// ... lines 22 - 37
}
}

Now, down here, copy these two lines, delete them, and write $issData = $cache->get(). The first argument should be the cache key, which we'll call... how about iss_location_data. The second argument should be an anonymous function (). Now we can paste the two lines we copied earlier below. But instead of setting the variable, let's just return. But before we can use this $client variable in an anonymous function, we need to use it. Write use($client): array.

40 lines | src/Controller/MainController.php
// ... lines 1 - 16
public function homepage(
// ... lines 18 - 20
): Response {
// ... lines 22 - 24
$issData = $cache->get('iss_location_data', function (ItemInterface $item) use ($client): array {
// ... lines 26 - 27
$response = $client->request('GET', 'https://api.wheretheiss.at/v1/satellites/25544');
return $response->toArray();
});
// ... lines 32 - 37
}
// ... lines 39 - 40

Debugging with the Cache Profiler

If we head over to our browser and refresh... we still made the HTTP Client request and, over here, we now have a cache icon that shows us if something was written in the cache. We have one! I'll click on this cache icon to open the profiler, and... how cool is that? We didn't create a custom pool for this so the default pool is being used, but we can create custom pools and we'll do that in a moment.

If we head back to the home page and refresh... the HTTP request is gone. And if we hover over the cache icon... nothing was written. And now, our page loads are noticeably faster. Right now, that data is cached forever unless we clear the cache, but for dev purposes, over in our function, let's change that. Add ItemInterface as the first argument and call it $item. Inside, write $item->expiresAfter() and pass time: 5.

40 lines | src/Controller/MainController.php
// ... lines 1 - 16
public function homepage(
// ... lines 18 - 20
): Response {
// ... lines 22 - 24
$issData = $cache->get('iss_location_data', function (ItemInterface $item) use ($client): array {
$item->expiresAfter(5);
// ... lines 27 - 30
});
// ... lines 32 - 37
}
// ... lines 39 - 40

This number is in seconds, after which the cache will expire. Back at our browser, if we refresh, nothing changes because the value was already cached. To see our changes, we need to clear it manually so it can be re-cached with our new time frame of five seconds.

Clearing the Cache

The default cache adapter is a file system, which means the cache is stored in the var/cache/dev/pools/ directory. Here, we can see our /app folder which corresponds to our app cache. We could delete this directory manually, but there's a better way. At your terminal, run:

bin/console cache:pool:list

This is the list of available pools in our application. To clear the cache.app pool, we can use another command:

bin/console cache:pool:clear cache.app

And... cache cleared! If we go back to our browser and refresh now...here's our HTTP request. If we quickly refresh again... now the data we have is coming from our cache. If we refresh one more time after five seconds have passed... here's our HTTP request again!

Next: Let's learn how to configure our cache service.