# State Providers

To retrieve data exposed by the API, API Platform uses classes called **state providers**.

With the Symfony variant, a state provider using [Doctrine
ORM](https://www.doctrine-project.org/projects/orm.html) is ready to retrieve data from a database and a state provider using
[Doctrine MongoDB ODM](https://www.doctrine-project.org/projects/mongodb-odm.html) to retrieve data from a document
database.

With the Laravel variant, a state provider using [Eloquent ORM](https://laravel.com/docs/eloquent) to retrieve data from a relational database and a state provider.

The ORM providers are enabled by default, based on your framework variant (Eloquent or Doctrine will be set up).


These state providers natively support paged collections and filters. They can be used as-is and are perfectly suited to common uses.

However, you sometimes want to retrieve data from other sources such as another persistence layer or a webservice.
Custom state providers can be used to do so. A project can include as many state providers as needed. The first able to
retrieve data for a given resource will be used.

To do so you need to implement the `ApiPlatform\State\ProviderInterface`.

In the following examples we will create custom state providers for Symfony entities and Laravel models:
- For Symfony we will create an entity class called `App\Entity\BlogPost`.
- For Laravel, we will create a model class called `App\Models\BlogPost`.

Note, that if your entity is not Doctrine-related or Eloquent-related, you need to flag the identifier property by using
`#[ApiProperty(identifier: true)` for things to work properly (see also [Entity Identifier Case](serialization.md#entity-identifier-case)).

## Creating a Custom State Provider

### Custom State Provider with Symfony

If the [Symfony MakerBundle](https://symfony.com/doc/current/bundles/SymfonyMakerBundle) is installed in your project,
you can use the following command to generate a custom state provider easily:

```console
bin/console make:state-provider
```

Let's start with a State Provider for the URI: `/blog_posts/{id}`.

First, your `BlogPostProvider` has to implement the
[`ProviderInterface`](https://github.com/api-platform/core/blob/main/src/State/ProviderInterface.php):

```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Entity\BlogPost;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;

/**
 * @implements ProviderInterface<BlogPost|null>
 */
final class BlogPostProvider implements ProviderInterface
{
    private array $data;

    public function __construct() {
        $this->data = [
            'ab' => new BlogPost('ab'),
            'cd' => new BlogPost('cd'),
        ];
    } 

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): BlogPost|null
    {
        return $this->data[$uriVariables['id']] ?? null;
    }
}
```

For the example, we store the list of our blog posts in an associative array `$data`.

As this operation expects a `BlogPost`, the `provide` methods return the instance of the `BlogPost` corresponding to the ID passed in the URL. If the ID doesn't exist in the associative array, `provide()` returns `null`. API Platform will automatically generate a 404 response if the provider returns `null`.

The `$uriVariables` parameter contains an array with the values of the URI variables.

To use this provider we need to configure the provider on the operation:

```php
<?php
// api/src/Entity/BlogPost.php

namespace App\Entity;

use ApiPlatform\Metadata\Get;
use App\State\BlogPostProvider;

#[Get(provider: BlogPostProvider::class)]
class BlogPost {}
```

Now let's say that we also want to handle the `/blog_posts` URI which returns a collection. We can change the Provider into
supporting a wider range of operations. Then we can provide a collection of blog posts when the operation is a `CollectionOperationInterface`:

```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Entity\BlogPost;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;
use ApiPlatform\Metadata\CollectionOperationInterface;

/**
 * @implements ProviderInterface<BlogPost[]|BlogPost|null>
 */
final class BlogPostProvider implements ProviderInterface
{
    private array $data;

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): iterable|BlogPost|null
    {
        if ($operation instanceof CollectionOperationInterface) {
            return $this->data;
        }

        return $this->data[$uriVariables['id']] ?? null;
    }
}
```

We then need to configure this same provider on the BlogPost `GetCollection` operation, or for every operation via the `ApiResource` attribute:

```php
<?php
// api/src/Entity/BlogPost.php

namespace App\Entity;

use ApiPlatform\Metadata\ApiResource;
use App\State\BlogPostProvider;

#[ApiResource(provider: BlogPostProvider::class)]
class BlogPost {}
```

#### Custom State Provider with Laravel

Using [Laravel Artisan Console](https://laravel.com/docs/artisan), you can generate a custom state provider easily with the following command:

```console
php artisan make:state-provider
```

Let's start with a State Provider for the URI: `/blog_posts/{id}`.

First, your `BlogPostProvider` has to implement the
[`ProviderInterface`](https://github.com/api-platform/core/blob/main/src/State/ProviderInterface.php):

```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Models\BlogPost;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;

/**
 * @implements ProviderInterface<BlogPost|null>
 */
final class BlogPostProvider implements ProviderInterface
{
    private array $data;

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): BlogPost|null
    {
        return $this->data[$uriVariables['id']] ?? null;
    }
}
```

For the example, we store the list of our blog posts in an associative array `$data`.

As this operation expects a `BlogPost`, the `provide` methods return the instance of the `BlogPost` corresponding to the ID passed in the URL. If the ID doesn't exist in the associative array, `provide()` returns `null`. API Platform will automatically generate a 404 response if the provider returns `null`.

The `$uriVariables` parameter contains an array with the values of the URI variables.

To use this provider we need to configure the provider on the operation:

```php
<?php
// api/src/Models/BlogPost.php

namespace App\Models;

use ApiPlatform\Metadata\Get;
use App\State\BlogPostProvider;

#[Get(provider: BlogPostProvider::class)]
class BlogPost {}
```

Now let's say that we also want to handle the `/blog_posts` URI which returns a collection. We can change the Provider into
supporting a wider range of operations. Then we can provide a collection of blog posts when the operation is a `CollectionOperationInterface`:

```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Models\BlogPost;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;
use ApiPlatform\Metadata\CollectionOperationInterface;

/**
 * @implements ProviderInterface<BlogPost[]|BlogPost|null>
 */
final class BlogPostProvider implements ProviderInterface
{
    private array $data;

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): iterable|BlogPost|null
    {
        if ($operation instanceof CollectionOperationInterface) {
            return $this->data;
        }

        return $this->data[$uriVariables['id']] ?? null;
    }
}
```

We then need to configure this same provider on the BlogPost `GetCollection` operation, or for every operation via the `ApiResource` attribute:

```php
<?php
// api/src/Models/BlogPost.php

namespace App\Models;

use ApiPlatform\Metadata\ApiResource;
use App\State\BlogPostProvider;

#[ApiResource(provider: BlogPostProvider::class)]
class BlogPost {}
```

## Hooking into the Built-In State Provider

If you want to execute custom business logic before or after retrieving data, this can be achieved by [decorating](https://symfony.com/doc/current/service_container/service_decoration.html) the built-in state providers or using [composition](https://en.wikipedia.org/wiki/Object_composition).

The next examples (one for  Symfony and one for Laravel) uses a [DTO](https://api-platform.com/docs/core/dto/#using-data-transfer-objects-dtos) to change the presentation for data originally retrieved by the default state provider.

### Symfony State Provider mechanism

```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Dto\AnotherRepresentation;
use App\Entity\Book;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;
use Symfony\Component\DependencyInjection\Attribute\Autowire;

/**
 * @implements ProviderInterface<AnotherRepresentation>
 */
final class BookRepresentationProvider implements ProviderInterface
{
    public function __construct(
        #[Autowire(service: 'api_platform.doctrine.orm.state.item_provider')]
        private ProviderInterface $itemProvider,
    )
    {
    }

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): AnotherRepresentation
    {
        $book = $this->itemProvider->provide($operation, $uriVariables, $context);

        return new AnotherRepresentation(
            // Add DTO constructor params here.
            // $book->getTitle(),
        );
    }
}
```

And configure that you want to use this provider on the Book resource:

```php
<?php
// api/src/Entity/Book.php

namespace App\Entity;

use ApiPlatform\Metadata\Get;
use App\Dto\AnotherRepresentation;
use App\State\BookRepresentationProvider;

#[Get(output: AnotherRepresentation::class, provider: BookRepresentationProvider::class)]
class Book {}
```

#### Laravel State Provider mechanism

First, don't forget to tag the service with the `ProviderInterface`

```php
<?php

namespace App\Providers;

use ApiPlatform\State\ProviderInterface;
use App\State\BookStateProvider;
use Illuminate\Support\ServiceProvider;

class AppServiceProvider extends ServiceProvider
{
    public function register(): void
    {
        $this->app->tag([BookRepresentationProvider::class], ProviderInterface::class);
    }

    public function boot(): void
    {
    }
}
```

After that, you can inject the `ProviderInterface`
```php
<?php
// api/src/State/BlogPostProvider.php

namespace App\State;

use App\Dto\AnotherRepresentation;
use App\Models\Book;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProviderInterface;
use Symfony\Component\DependencyInjection\Attribute\Autowire;

/**
 * @implements ProviderInterface<AnotherRepresentation>
 */
final class BookRepresentationProvider implements ProviderInterface
{
    public function __construct(
        private ProviderInterface $itemProvider,
    )
    {
    }
    
    public function provide(Operation $operation, array $uriVariables = [], array $context = []): AnotherRepresentation
    {
        $book = $this->itemProvider->provide($operation, $uriVariables, $context);
        
        return new AnotherRepresentation(
            // Add DTO constructor params here.
            // $book->getTitle(),
        );
    }
}
```

And configure that you want to use this provider on the Book resource:

```php
<?php
// api/app/Models/Book.php

namespace App\Models;

use ApiPlatform\Metadata\Get;
use App\Dto\AnotherRepresentation;
use App\State\BookRepresentationProvider;

#[Get(output: AnotherRepresentation::class, provider: BookRepresentationProvider::class)]
class Book {}
```


## Registering Services Without Autowiring (only for the Symfony variant)

The services in the previous examples are automatically registered because
[autowiring](https://symfony.com/doc/current/service_container/autowiring.html)
and autoconfiguration are enabled by default in API Platform.
To declare the service explicitly, you can use the following snippet:

```yaml
# api/config/services.yaml

services:
    # ...
    App\State\BlogPostProvider: ~
        tags: [ 'api_platform.state_provider' ]

# api/config/services.yaml
services:
    # ...
    App\State\BookRepresentationProvider:
        arguments:
            $itemProvider: '@api_platform.doctrine.orm.state.item_provider'
        tags: [ 'api_platform.state_provider' ]
```