> APIs > API Platform 3 Part 3: Custom Resources
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16.

stateOptions + entityClass Magic

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When we create a non-entity API resource, we're responsible for loading and saving the data. What's frustrating is that, if we make a custom state provider for UserApi, it will do the exact same thing as the core Doctrine state provider: query the database. It's a bummer to reinvent all of that logic ourselves. This, historically, has been the Achille's heel of DTO's.

Checking out the Core CollectionProvider

Crack open the core CollectionProvider from Doctrine ORM. If you ever wanted to see what the CollectionProvider looks like, here it is! It's more complex than I imagined. It creates the QueryBuilder, calls handleLinks() (which intelligently joins to other tables based on the data you need), and houses the query extension system. In the last tutorial, we created a query extension for DragonTreasure so it would only return published items. And part of that extension system, though we can't see it here, is where pagination and filtering is added.

So, this class gives us a lot... and I want to reuse it. So, darn it, let's yolo this thing and try to!

Trying to use the CollectionProvider

Head over to UserApi, say provider, and point to CollectionProvider (the one from Doctrine ORM).

16 lines | src/ApiResource/UserApi.php
// ... lines 1 - 4
use ApiPlatform\Doctrine\Orm\State\CollectionProvider;
// ... lines 6 - 7
#[ApiResource(
shortName: 'User',
provider: CollectionProvider::class,
)]
class UserApi
{
public ?int $id = null;
}

Let's see what happens! At the browser, go to the endpoint directly - /api/users.jsonld. And... we get an error:

Call to a member function getRepository() on null.

Coming from the core CollectionProvider. Boo. But not surprising. Our UserApi isn't an entity... and so when it tries to figure out how to query for it, explosions!

Hello stateOptions + entityClas

But psst... want to hear a secret? There is a way we can hint to the provider that data for this class should come from the User entity. It looks like this: stateOptions set it to a new Options object (making sure to grab the one from ORM), and inside, entityClass: User::class.

19 lines | src/ApiResource/UserApi.php
// ... lines 1 - 4
use ApiPlatform\Doctrine\Orm\State\CollectionProvider;
use ApiPlatform\Doctrine\Orm\State\Options;
// ... line 7
use App\Entity\User;
#[ApiResource(
shortName: 'User',
provider: CollectionProvider::class,
stateOptions: new Options(entityClass: User::class),
)]
class UserApi
{
public ?int $id = null;
}

Let's see what happens now! When we head over and refresh... whoa! It looks like that worked! We see "totalItems: 11"... with items 1-11 all right here. We only have an $id property, but I guess that makes sense... since we only have an $id property inside our UserApi.

Let's add a few more properties! How about public ?string $email = null and public ?string $username = null. Both of these properties also live in our User entity.

23 lines | src/ApiResource/UserApi.php
// ... lines 1 - 14
class UserApi
{
public ?int $id = null;
public ?string $email = null;
public ?string $username = null;
}

When we refresh... those pop up too! This is working.... but how? What the heck is going on?

How this all Works

If we could peek under API Platform's hood, we would see that the underlying API resource objects are UserApi. So what we're seeing here is the JSON for a collection of UserApi objects.

But there are several places in the system that look for stateOptions and, if it's present, will use the entityClass from that. The CollectionProvider we opened a moment ago - the one from Doctrine ORM - is one of those cases. It grabs the entityClass from stateOptions if there is one... then uses that when it does the query.

In fact, as soon as we have this stateOptions + entityClass thing, API Platform sets the provider and the processor automatically to the core Doctrine ones. So we don't even need to have the provider key: it's set for us.

21 lines | src/ApiResource/UserApi.php
// ... lines 1 - 8
#[ApiResource(
shortName: 'User',
stateOptions: new Options(entityClass: User::class),
)]
class UserApi
{
// ... lines 15 - 19
}

Okay, but if the provider is querying for User entity objects, how and when is that converted to UserApi objects... so that they can be serialized to JSON? The answer is during serialization... and it's a bid odd. Thanks to stateOptions, API Platform is actually serializing the User entity object. But to get the list of the properties that it should serialize, it reads the metadata from UserApi. Then, it grabs the property values from User... and puts them onto a UserApi instance. Essentially, it serializes the User entity into a UserApi object... and then to JSON.

This seems to work well... but with one, major limitation.

Limitation: No Custom Properties

Add a property that is not on our entity, like public int $flameThrowingDistance = 0. There is no $flameThrowingDistance property over on User.

23 lines | src/ApiResource/UserApi.php
// ... lines 1 - 12
class UserApi
{
// ... lines 15 - 20
public int $flameThrowingDistance = 0;
}

When we try this... explosion! If we scroll down a bit, we see that this comes from the normalizer system... which is part of the serializer. It looks at UserApi, thinks "Oh, I need a $flameThrowingDistance field", tries to fetch that from User, and, since it's not there, boom!

So the colossal, monstrous, titanic limitation of the entityClass strategy is... we can't have extra fields on our UserApi class. But no worries: we'll find a path around this in the next chapter. For now, remove the extra property.

Oh, and one other limitation that you may have noticed is that we don't have the JSON-LD fields @id or @type. We'll handle that while we're fixing the issue with custom fields... like the multitasking wizards we are.

Adding a Relation Property

Let's add another property: public array $dragonTreasures = []? We do have a $dragonTreasures property over on User that holds a collection of DragonTreasure objects.

23 lines | src/ApiResource/UserApi.php
// ... lines 1 - 12
class UserApi
{
// ... lines 15 - 19
public array $dragonTreasures = [];
}

So if we go over and test this out... it works fine! Though, surprisingly, it's embedding the dragonTreasures instead of returning them as IRIs. This is the same problem we saw earlier, and the fix is the same.

I do want to point out one interesting thing about this, though. When it embeds the dragonTreasures, one of the properties is owner. Right now, that owner is actually the User entity. Since the User entity is no longer an API resource, it adds this random genid thing.

I'll talk about this more in a bit, but once we start creating DTOs and using those instead of entities, we'll probably want to use DTOs for all of our API resources... instead of mixing entities and DTOs... because it creates issues like this.

Anyway, fix this by advertising that this is an array of DragonTreasure. I'm using a slightly different array syntax there, but it doesn't really matter.

27 lines | src/ApiResource/UserApi.php
// ... lines 1 - 6
use App\Entity\DragonTreasure;
// ... lines 8 - 13
class UserApi
{
// ... lines 16 - 21
/**
* @var array<int, DragonTreasure>
*/
public array $dragonTreasures = [];
}

If we try this again... back to IRIs! Woo!

Built-in Pagination

So far, we know that stateOptions does three things. One: It automatically sets the provider and processor to use the core Doctrine provider and processor. Two: the provider is smart enough to query from this entity. This also works for single items, like /users/1.jsonld. And three: The serializer serializes the User entity into a UserApi object.

The fact that stateOptions causes the core Doctrine state provider to be used has some very important other side effects. First, we get pagination for free. Add paginationItemsPerPage: 5, go over, and refresh. We see that the total number of items is "11"... but it only shows five... and the pages are down here.

28 lines | src/ApiResource/UserApi.php
// ... lines 1 - 9
#[ApiResource(
shortName: 'User',
paginationItemsPerPage: 5,
stateOptions: new Options(entityClass: User::class),
)]
class UserApi
{
// ... lines 17 - 26
}

Second, the collection provider also makes the query extension system work. We don't have any query extensions for User, but we do have one for DragonTreasure. Later on, when we convert DragonTreasure to its own DTO class, this extension is still going to work.

The third and final goodie is that the filter system still works! Watch: above UserApi, add #[ApiFilter()] with SearchFilter::class and properties: with username set to partial.

33 lines | src/ApiResource/UserApi.php
// ... lines 1 - 4
use ApiPlatform\Doctrine\Orm\Filter\SearchFilter;
// ... line 6
use ApiPlatform\Metadata\ApiFilter;
// ... lines 8 - 16
#[ApiFilter(SearchFilter::class, properties: [
'username' => 'partial',
])]
class UserApi
{
// ... lines 22 - 31
}

Go back and look at the documentation... whoops. I autocompleted the SearchFilter from ODM. Delete that, then I'll hit Alt+Enter to grab the one from ORM.

Refresh the docs again... and look at the /api/users endpoint. It is advertising that there's a username filter, and it is going to work! In the other tab, add ?username=Clumsy.

And... yes! It only returns those 5 results! So the filter system works! Though, one thing to note is that, when we say username, we're referring to the $username property on the User entity. As far as the filter is concerned, we don't even need a username in UserApi.

So: we're reusing all of this core Doctrine provider logic, we have pagination, filters and.... it's the best thing since ice cream sandwiches. Except... for that big, scary limitation: that our DTO can't have custom fields. And... that's really the whole point of a DTO: to gain the flexibility of having different fields than your entity. So let's see how to fix that limitation next.