custom_constraint.rst

.. index::
   single: Validation; Custom constraints

How to create a Custom Validation Constraint

You can create a custom constraint by extending the base constraint class, :class:`Symfony\\Component\\Validator\\Constraint`. Options for your constraint are represented as public properties on the constraint class. For example, the :doc:`Url</reference/constraints/Url>` constraint includes the message and protocols properties:

namespace Symfony\Component\Validator\Constraints;

use Symfony\Component\Validator\Constraint;

/**
 * @Annotation
 */
class Url extends Constraint
{
    public $message = 'This value is not a valid URL';
    public $protocols = array('http', 'https', 'ftp', 'ftps');
}

Note

The @Annotation annotation is necessary for this new constraint in order to make it available for use in classes via annotations.

As you can see, a constraint class is fairly minimal. The actual validation is performed by a another "constraint validator" class. The constraint validator class is specified by the constraint's validatedBy() method, which includes some simple default logic:

// in the base Symfony\Component\Validator\Constraint class
public function validatedBy()
{
    return get_class($this).'Validator';
}

In other words, if you create a custom Constraint (e.g. MyConstraint), Symfony2 will automatically look for another class, MyConstraintValidator when actually performing the validation.

The validator class is also simple, and only has one required method: isValid. Take the NotBlankValidator as an example:

class NotBlankValidator extends ConstraintValidator
{
    public function isValid($value, Constraint $constraint)
    {
        if (null === $value || '' === $value) {
            $this->setMessage($constraint->message);

            return false;
        }

        return true;
    }
}

Constraint Validators with Dependencies

If your constraint validator has dependencies, such as a database connection, it will need to be configured as a service in the dependency injection container. This service must include the validator.constraint_validator tag and an alias attribute:

.. configuration-block::

    .. code-block:: yaml

        services:
            validator.unique.your_validator_name:
                class: Fully\Qualified\Validator\Class\Name
                tags:
                    - { name: validator.constraint_validator, alias: alias_name }

    .. code-block:: xml

        <service id="validator.unique.your_validator_name" class="Fully\Qualified\Validator\Class\Name">
            <argument type="service" id="doctrine.orm.default_entity_manager" />
            <tag name="validator.constraint_validator" alias="alias_name" />
        </service>

    .. code-block:: php

        $container
            ->register('validator.unique.your_validator_name', 'Fully\Qualified\Validator\Class\Name')
            ->addTag('validator.constraint_validator', array('alias' => 'alias_name'))
        ;

Your constraint class may now use this alias to reference the appropriate validator:

public function validatedBy()
{
    return 'alias_name';
}