When

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6.2

The When constraint was introduced in Symfony 6.2.

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
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;

    // ...
}

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 1 or 2 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).

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
    {
        // ...
    }
}

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.

6.4

Passing a single Constraint instead of an array was introduced in Symfony 6.4.

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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