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20.

Performance Optimization 1: Memoization

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Our Twig filter is working as expected, and we're using it here in our article index. Right now, we're overriding the article variable with its translated version at the start of the loop. I think there's another valid way to use this filter - only when we need it.

Using the Filter Only When Needed

First, delete the set article override. Then, down here, where we actually need the translated version - for title and content. Change article.title to article|translate_object.title and do the same for content: article|translate_object.content:

88 lines | templates/article/index.html.twig
// ... lines 1 - 2
{% block body %}
// ... line 4
<div class="">
// ... line 6
<div>
{% for article in articles %}
<div class="bg-white my-2 rounded-2xl p-5">
<a href="{{ path('app_article_show', {slug: article.slug}) }}">
<div class="flex flex-col md:flex-row">
// ... lines 12 - 14
<div class="text-5xl font-medium mt-4">{{ article|translate_object.title }}</div>
<div class="line-clamp-3 my-5">{{ article|translate_object.content|markdown_to_html }}</div>
// ... lines 17 - 21
</div>
</a>
</div>
{% endfor %}
</div>
// ... lines 27 - 85
</div>
{% endblock %}

Jump back to our browser - we're on the French homepage. Before refreshing, notice the query count in the web debug toolbar. 4, one query to fetch all articles, and then one query per article to grab translations. Now refresh the page. Ok, all still works... but look at that query count - 7! One query for all articles, and now two queries per article. The translated values are being loaded twice, even though they're identical.

Let's fix this with a technique called memoization. This is a fancy word, and I really like saying it, but it just means storing data in memory to prevent redundant processing.

WeakMap

We'll implement this in our ObjectTranslator, so open that up. We could just add an array property to store translated objects by ID or something, but this could lead to memory leaks. In long-running processes, this array could grow indefinitely.

Instead, we'll use a special PHP core object called a WeakMap. Add a new property, private \WeakMap $translatedObjects:

82 lines | object-translation-bundle/src/ObjectTranslator.php
// ... lines 1 - 9
final class ObjectTranslator
{
private \WeakMap $translatedObjects;
// ... lines 13 - 80
}

This is like an array, but it's keyed by objects, not strings or integers like you're used to. In PHP, when an object is created and passed around, it's actually a reference to that object. As long as something is using that object, it stays in memory. When nothing is using it anymore, PHP automatically cleans it up. If we used a standard array to store translated objects, that reference would never be removed. A WeakMap is different, it holds the object but doesn't prevent it from being cleaned up - a weak reference. This is perfect for our use case!

To use it, we need to instantiate it first, so in the constructor, $this->translatedObjects = new \WeakMap():

82 lines | object-translation-bundle/src/ObjectTranslator.php
// ... lines 1 - 9
final class ObjectTranslator
{
// ... lines 12 - 13
public function __construct(
// ... lines 15 - 18
) {
$this->translatedObjects = new \WeakMap();
}
// ... lines 22 - 80
}

Down in the translate() method, this translationFor() call is expensive, it's making a database query. So, let's save this whole TranslatedObject in our WeakMap. Right after return, write $this->translatedObjects - what to key it by? The original $object! Now, use the null coalescing assignment operator ??= and then create the TranslatedObject:

82 lines | object-translation-bundle/src/ObjectTranslator.php
// ... lines 1 - 9
final class ObjectTranslator
{
// ... lines 12 - 29
public function translate(object $object): object
{
// ... lines 32 - 37
return $this->translatedObjects[$object] ??= new TranslatedObject($object, $this->translationsFor($object, $locale));
}
// ... lines 40 - 80
}

This checks if the translated object is already in the weak map (for the original object). If so, return that. Otherwise, create a new TranslatedObject, store it in the weak map, and return it. If the original object is cleaned up by PHP, it'll automatically be removed from the weak map.

Let's see it in action! Back in your browser, we see the 7 queries. Now refresh... still works... and look at the query count - back to 4! The memoization is working!

Next, let's continue this performance optimization process with non-memory caching.