# Validation

API Platform Core uses the [Symfony Validator component](http://symfony.com/doc/current/book/validation.html) to validate
entities.

Without specific configuration, it uses the default validation group, but this behavior is customizable.

## Using Validation Groups

Built-in actions are able to leverage Symfony's [validation groups](http://symfony.com/doc/current/book/validation.html#validation-groups).

You can customize them by editing the resource configuration and add the groups you want to use when the validation occurs:

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

use ApiPlatform\Core\Annotation\ApiResource;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ApiResource(attributes={"validation_groups"={"a", "b"}})
 */
class Book
{
    /**
     * @Assert\NotBlank(groups={"a"})
     */
    private $name;

    /**
     * @Assert\NotNull(groups={"b"})
     */
    private $author;

    // ...
}
```

With the previous configuration, the validations groups `a` and `b` will be used when validation is performed.

Like for [serialization groups](serialization.md#using-different-serialization-groups-per-operation),
you can specify validation groups globally or on a per operation basis.

Of course, you can use XML or YAML configuration format instead of annotations if you prefer.

You may also pass in a [group sequence](http://symfony.com/doc/current/validation/sequence_provider.html) in place of
the array of group names.

## Dynamic Validation Groups

If you need to dynamically determine which validation groups to use for an entity in different scenarios, just pass in a
[callable](http://php.net/manual/en/language.types.callable.php). The callback will receive the entity object as its first
argument, and should return an array of group names or a [group sequence](http://symfony.com/doc/current/validation/sequence_provider.html).

In the following example, we use a static method to return the validation groups:

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

use ApiPlatform\Core\Annotation\ApiResource;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ApiResource(
 *     attributes={"validation_groups"={Book::class, "validationGroups"}}
 * )
 */
class Book
{
    /**
     * Return dynamic validation groups.
     *
     * @param self $book Contains the instance of Book to validate.
     *
     * @return string[]
     */
    public static function validationGroups(self $book)
    {
        return ['a'];
    }

    /**
     * @Assert\NotBlank(groups={"a"})
     */
    private $name;

    /**
     * @Assert\NotNull(groups={"b"})
     */
    private $author;

    // ...
}
```

Alternatively, you can use a service to retrieve the groups to use:

```php
<?php
// src/AppBundle/Validator/AdminGroupsGenerator.php

namespace AppBundle\Validator;

use AppBundle\Entity\Book;
use Symfony\Component\Security\Core\Authorization\AuthorizationCheckerInterface;

final class AdminGroupsGenerator
{
    private $authorizationChecker;

    public function __construct(AuthorizationCheckerInterface $authorizationChecker)
    {
        $this->authorizationChecker = $authorizationChecker;
    }

    public function __invoke(Book $book): array
    {
        return $this->authorizationChecker->isGranted('ROLE_ADMIN', $book) ? ['a', 'b'] : ['a'];
    }
}
```

This class selects the groups to apply regarding the role of the current user: if the current user has the `ROLE_ADMIN` role, groups `a` and `b` are returned. In other cases, just `a` is returned.

This class is automatically registered as a service thanks to [the autowiring feature of the Symfony Dependency Injection Component](https://symfony.com/doc/current/service_container/autowiring.html). Just note that this service must be public.

Then, configure the entity class to use this service to retrieve validation groups:

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

namespace AppBundle\Entity;

use ApiPlatform\Core\Annotation\ApiResource;
use AppBundle\Validator\AdminGroupsGenerator;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * @ApiResource(attributes={"validation_groups"=AdminGroupsGenerator::class})
 */
class Book
{
    /**
     * @Assert\NotBlank(groups={"a"})
     */
    private $name;

    /**
     * @Assert\NotNull(groups={"b"})
     */
    private $author;

    // ...
}
```