> APIs > API Platform 3 Part 1: Mythically Good RESTful APIs
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14.

PropertyFilter: Sparse Fieldsets

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Since dragons love expensive treasure, let's add a way for them to filter based on the value, like within a range. There's a built-in filter for that called RangeFilter. Find the $value property and, like we did before, use #[ApiFilter()] and inside RangeFilter (the one from ORM) ::class:

171 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 6
use ApiPlatform\Doctrine\Orm\Filter\RangeFilter;
// ... lines 8 - 40
class DragonTreasure
{
// ... lines 43 - 62
#[ApiFilter(RangeFilter::class)]
private ?int $value = null;
// ... lines 65 - 169
}

This one doesn't need any other options, so... we're done! Dang... that was easy. When we refresh... open it up, and hit "Try it out".... look at that! We have a ton of new filters - value[between], value[gt] (or "greater than"), value[gte], etc. Let's try value[gt]... with a random number... maybe 500000. When we click "Execute"... yup! It updated the URL here. It's... not the prettiest URL ever - due to the encoding - but it works like a charm. And down in the results... apparently there are 18 treasures worth more than that!

PropertyFilter

The last filter I want to show you... isn't really a filter at all. It's a way our API clients to choose which fields they want returned... instead of which results.

To show this off, find the getDescription() method. Pretend that we want to return a shorter, truncated version of the description. To do this, copy the getDescription() method, paste it below, and rename it to getShortDescription():

178 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 41
class DragonTreasure
{
// ... lines 44 - 99
public function getShortDescription(): string
{
// ... line 102
}
// ... lines 104 - 176
}

To truncate this, we can use the u() function from Symfony. Type u and make sure to hit "tab" to autocomplete that. This is a rare function that Symfony gives us... and hitting "tab" did add a use statement for it:

178 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 20
use function Symfony\Component\String\u;
// ... lines 22 - 41
class DragonTreasure
{
// ... lines 44 - 99
public function getShortDescription(): string
{
return u($this->getDescription())->truncate(40, '...');
}
// ... lines 104 - 176
}

This creates an object with all sorts of string-related goodies on it, including truncate(). Pass 40 to truncate at 40 characters followed by ....

Method done! To expose this to our API, above, add the Groups attribute with treasure:read:

178 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 20
use function Symfony\Component\String\u;
// ... lines 22 - 41
class DragonTreasure
{
// ... lines 44 - 98
#[Groups(['treasure:read'])]
public function getShortDescription(): string
{
return u($this->getDescription())->truncate(40, '...');
}
// ... lines 104 - 176
}

Beautiful! Okay, head back to the documentation and refresh. Open the GET endpoint, hit "Try it out", "Execute" and... nice. Here's our truncated description!

Though... it is weird that we now return two descriptions: a short one and the regular one. If our API client wants the short description, it may not want us to also return the full-length description... for the sake of bandwidth.

What can we do? Introducing: the PropertyFilter! Head back to DragonTreasure. Unlike the others, this filter must go above the class. So right here, say ApiFilter, and then PropertyFilter (in this case, there's only one of them) ::class. There are some options you can pass to this - which you can find in the docs - but we don't need any of them:

180 lines | src/Entity/DragonTreasure.php
// ... lines 1 - 14
use ApiPlatform\Serializer\Filter\PropertyFilter;
// ... lines 16 - 42
#[ApiFilter(PropertyFilter::class)]
class DragonTreasure
{
// ... lines 46 - 178
}

So... what does that do? Head back, refresh the documentation, open up the GET collection endpoint, and hit "Try it out". Woh! We now see a properties[] box and we can add items to it. Let's try it! Add a new string called name and another called description.

Moment of truth. Hit "Execute", and... there it is! It popped these onto the URL like normal. But look at the response: it only contains the name and description fields. Well... it also contains the JSON-LD fields, but the real data is just those two fields.

If we removed the properties strings, we would get the normal, full response. So, by default, you get all fields. But users can now choose fewer fields if they want to.

What about Vulcain?

This all works quite nicely. But if you look at the API Platform documentation for the PropertyFilter, they actually recommend a different solution: something called "Vulcain". Nope, not Spock's home planet. We're talking about a protocol that adds features to your web server. It was created by the API Platform team, and if we scroll down a bit, they have a really good example.

Pretend that we have the following API. If we make a request to /books, we get these two books back. Simple enough. Then maybe we want to get more info about the first book, so we make a request to that URL - /books/1. Great! But... now we want details about the author, so we make a request to /authors/1.

So, to get all the book information and all the author information, we ultimately needed to make four requests: the original, plus 3 more. That's not great for performance.

What Vulcain allows you to do is just make this first request... but tell the server that it should push the data from the other requests to you.

We can see this best in JavaScript, and there's a little example down here. In this case, imagine that we're making a request to /books/1 but we know that we also need the author information. So, when we make the request, we include a special Preload header. This tells the server:

Hey! After returning the book data, use a server push to send me the information found by following the author IRI.

The really cool thing is that your JavaScript doesn't really change. You still use fetch() to make a second request to the bookJSON.author URL... except that this will return instantly because the browser already has the data.

I'm not going to get into all the specifics, but the Preload on the first example is even more impressive: /member/*/author. That tells the server to push all the data as if we had also requested each of the member keys - so all the books - and their author URLs.

The point is: if you use Vulcain, your API users can make tiny changes to enjoy huge performance benefits... without us needing to add a lot of fanciness to our API.

Next: Let's talk about formats. We know that our API can return JSON-LD, JSON, and even HTML representations of our resources. Let's add two new formats, including a CSV format, which will be the fastest CSV export feature you've ever built.