When

This constraint allows you to apply constraints validation only if the provided expression returns true. See Basic Usage for an example.

Applies to	class or property/method
Options	expression constraints groups payload values
Class	When
Validator	WhenValidator

Basic Usage

Imagine you have a class Discount with type and value properties:

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        // src/Model/Discount.php
namespace App\Model;

class Discount
{
    private ?string $type;

    private ?int $value;

    // ...

    public function getType(): ?string
    {
        return $this->type;
    }

    public function getValue(): ?int
    {
        return $this->value;
    }
}
    

To validate the object, you have some requirements:

A) If type is percent, then value must be less than or equal 100; B) If type is absolute, then value can be anything; C) No matter the value of type, the value must be greater than 0.

One way to accomplish this is with the When constraint:

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        // src/Model/Discount.php
namespace App\Model;

use Symfony\Component\Validator\Constraints as Assert;

class Discount
{
    #[Assert\GreaterThan(0)]
    #[Assert\When(
        expression: 'this.getType() == "percent"',
        constraints: [
            new Assert\LessThanOrEqual(100, message: 'The value should be between 1 and 100!')
        ],
    )]
    private ?int $value;

    // ...
}
    

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        # config/validator/validation.yaml
App\Model\Discount:
    properties:
        value:
            - GreaterThan: 0
            - When:
                expression: "this.getType() == 'percent'"
                constraints:
                    - LessThanOrEqual:
                        value: 100
                        message: "The value should be between 1 and 100!"
    

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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\Model\Discount">
        <property name="value">
            <constraint name="GreaterThan">0</constraint>
            <constraint name="When">
                <option name="expression">
                    this.getType() == 'percent'
                </option>
                <option name="constraints">
                    <constraint name="LessThanOrEqual">
                        <option name="value">100</option>
                        <option name="message">The value should be between 1 and 100!</option>
                    </constraint>
                </option>
            </constraint>
        </property>
    </class>
</constraint-mapping>
    

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        // src/Model/Discount.php
namespace App\Model;

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

class Discount
{
    public static function loadValidatorMetadata(ClassMetadata $metadata): void
    {
        $metadata->addPropertyConstraint('value', new Assert\GreaterThan(0));
        $metadata->addPropertyConstraint('value', new Assert\When([
            'expression' => 'this.getType() == "percent"',
            'constraints' => [
                new Assert\LessThanOrEqual([
                    'value' => 100,
                    'message' => 'The value should be between 1 and 100!',
                ]),
            ],
        ]));
    }

    // ...
}
    

The expression option is the expression that must return true in order to trigger the validation of the attached constraints. To learn more about the expression language syntax, see The Expression Syntax.

For more information about the expression and what variables are available to you, see the expression option details below.

Options

`expression`

type: string

The condition written with the expression language syntax that will be evaluated. If the expression evaluates to a falsey value (i.e. using ==, not ===), validation of constraints won't be triggered.

To learn more about the expression language syntax, see The Expression Syntax.

Depending on how you use the constraint, you have access to different variables in your expression:

this: The object being validated (e.g. an instance of Discount).
value: The value of the property being validated (only available when the constraint is applied to a property).
context: The ExecutionContextInterface object that provides information such as the currently validated class, the name of the currently validated property, the list of violations, etc.

7.2

The context variable in expressions was introduced in Symfony 7.2.

The value variable can be used when you want to execute more complex validation based on its value:

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        // src/Model/Discount.php
namespace App\Model;

use Symfony\Component\Validator\Constraints as Assert;
use Symfony\Component\Validator\Context\ExecutionContextInterface;

class Discount
{
    #[Assert\When(
        expression: 'value == "percent"',
        constraints: [new Assert\Callback('doComplexValidation')],
    )]
    private ?string $type;
    // ...

    public function doComplexValidation(ExecutionContextInterface $context, $payload): void
    {
        // ...
    }
}
    

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        # config/validator/validation.yaml
App\Model\Discount:
    properties:
        type:
            - When:
                expression: "value == 'percent'"
                constraints:
                    - Callback: doComplexValidation
    

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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\Model\Discount">
        <property name="type">
            <constraint name="When">
                <option name="expression">
                    value == 'percent'
                </option>
                <option name="constraints">
                    <constraint name="Callback">
                        <option name="callback">doComplexValidation</option>
                    </constraint>
                </option>
            </constraint>
        </property>
    </class>
</constraint-mapping>
    

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        // src/Model/Discount.php
namespace App\Model;

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

class Discount
{
    // ...

    public static function loadValidatorMetadata(ClassMetadata $metadata): void
    {
        $metadata->addPropertyConstraint('type', new Assert\When([
            'expression' => 'value == "percent"',
            'constraints' => [
                new Assert\Callback('doComplexValidation'),
            ],
        ]));
    }

    public function doComplexValidation(ExecutionContextInterface $context, $payload): void
    {
        // ...
    }
}
    

You can also pass custom variables using the values option.

`constraints`

type: array|Constraint

One or multiple constraints that are applied if the expression returns true.

`groups`

type: array | string default: null

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

`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.

`values`

type: array default: []

The values of the custom variables used in the expression. Values can be of any type (numeric, boolean, strings, null, etc.)

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.

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