Presence and Absence of Fields

By default, this constraint validates more than whether or not the individual fields in the collection pass their assigned constraints. In fact, if any keys of a collection are missing or if there are any unrecognized keys in the collection, validation errors will be thrown.

If you would like to allow for keys to be absent from the collection or if you would like "extra" keys to be allowed in the collection, you can modify the allowMissingFields and allowExtraFields options respectively. In the above example, the allowMissingFields option was set to true, meaning that if either of the personal_email or short_bio elements were missing from the $personalData property, no validation error would occur.

Required and Optional Field Constraints

Constraints for fields within a collection can be wrapped in the Required or Optional constraint to control whether they should always be applied (Required) or only applied when the field is present (Optional).

For instance, if you want to require that the personal_email field of the profileData array is not blank and is a valid email but the alternate_email field is optional but must be a valid email if supplied, you can do the following:

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// src/Entity/Author.php
namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;

class Author
{
    #[Assert\Collection(
        fields: [
            'personal_email' => new Assert\Required([
                new Assert\NotBlank,
                new Assert\Email,
            ]),
            'alternate_email' => new Assert\Optional(
                new Assert\Email
            ),
        ],
    )]
    protected $profileData = ['personal_email' => 'email@example.com'];
}

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# config/validator/validation.yaml
App\Entity\Author:
    properties:
        profile_data:
            - Collection:
                fields:
                    personal_email:
                        - Required:
                            - NotBlank: ~
                            - Email: ~
                    alternate_email:
                        - Optional:
                            - Email: ~

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<!-- config/validator/validation.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping https://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">

    <class name="App\Entity\Author">
        <property name="profile_data">
            <constraint name="Collection">
                <option name="fields">
                    <value key="personal_email">
                        <constraint name="Required">
                            <constraint name="NotBlank"/>
                            <constraint name="Email"/>
                        </constraint>
                    </value>
                    <value key="alternate_email">
                        <constraint name="Optional">
                            <constraint name="Email"/>
                        </constraint>
                    </value>
                </option>
            </constraint>
        </property>
    </class>
</constraint-mapping>

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// src/Entity/Author.php
namespace App\Entity;

use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Mapping\ClassMetadata;

class Author
{
    protected $profileData = ['personal_email'];

    public static function loadValidatorMetadata(ClassMetadata $metadata)
    {
        $metadata->addPropertyConstraint('profileData', new Assert\Collection([
            'fields' => [
                'personal_email'  => new Assert\Required([
                    new Assert\NotBlank(),
                    new Assert\Email(),
                ]),
                'alternate_email' => new Assert\Optional(new Assert\Email()),
            ],
        ]));
    }
}

Even without allowMissingFields set to true, you can now omit the alternate_email property completely from the profileData array, since it is Optional. However, if the personal_email field does not exist in the array, the NotBlank constraint will still be applied (since it is wrapped in Required) and you will receive a constraint violation.

When you define groups in nested constraints they are automatically added to the Collection constraint itself so it can be traversed for all nested groups. Take the following example:

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use Symfony\Component\Validator\Constraints as Assert;

$constraint = new Assert\Collection([
    'fields' => [
        'name' => new Assert\NotBlank(['groups' => 'basic']),
        'email' => new Assert\NotBlank(['groups' => 'contact']),
    ],
]);

This will result in the following configuration:

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$constraint = new Assert\Collection([
    'fields' => [
        'name' => new Assert\Required([
            'constraints' => new Assert\NotBlank(['groups' => 'basic']),
            'groups' => ['basic', 'strict'],
        ]),
        'email' => new Assert\Required([
            "constraints" => new Assert\NotBlank(['groups' => 'contact']),
            'groups' => ['basic', 'strict'],
        ]),
    ],
    'groups' => ['basic', 'strict'],
]);

The default allowMissingFields option requires the fields in all groups. So when validating in contact group, $name can be empty but the key is still required. If this is not the intended behavior, use the Optional constraint explicitly instead of Required.

allowExtraFields

type: boolean default: false

If this option is set to false and the underlying collection contains one or more elements that are not included in the fields option, a validation error will be returned. If set to true, extra fields are OK.

allowMissingFields

type: boolean default: false

If this option is set to false and one or more fields from the fields option are not present in the underlying collection, a validation error will be returned. If set to true, it's OK if some fields in the fields option are not present in the underlying collection.

extraFieldsMessage

type: string default: This field was not expected.

The message shown if allowExtraFields is false and an extra field is detected.

You can use the following parameters in this message:

fields

type: array [default option]

This option is required and is an associative array defining all of the keys in the collection and, for each key, exactly which validator(s) should be executed against that element of the collection.

groups

type: array | string default: null

It defines the validation group or groups of this constraint. Read more about validation groups.

missingFieldsMessage

type: string default: This field is missing.

The message shown if allowMissingFields is false and one or more fields are missing from the underlying collection.

You can use the following parameters in this message:

payload

type: mixed default: null

This option can be used to attach arbitrary domain-specific data to a constraint. The configured payload is not used by the Validator component, but its processing is completely up to you.

For example, you may want to use several error levels to present failed constraints differently in the front-end depending on the severity of the error.