Validation in web applications is a very crucial topic: Almost all data which is entered by an end user needs some checking rules, no matter if he enters an e-mail address or a subject for a forum posting.

While validation itself is quite simple, embedding it into the rest of the framework is not: If the user has entered a wrong value, the original page has to be re-displayed, and the user needs some well-readable information on what data he should enter.

This chapter explains:

  • how to use the validators being part of Flow
  • how to write your own validators
  • how to use validation in your own code
  • how validation is embedded in the model, the persistence and the MVC layer

Automatic Validation Throughout The Framework

Inside Flow, validation is triggered automatically at two places: When an object is persisted, its base validators are checked as explained in the last section. Furthermore, validation happens in the MVC layer when a Domain Model is used as a controller argument, directly after Property Mapping.


If a validation error occurs during persistence, there is no way to catch this error and handle it – as persistence is executed at the end of every request after the response has been sent to the client.

Thus, validation on persistence is merely a safeguard for preventing invalid data to be stored in the database.

When validation in the MVC layer happens, it is possible to handle errors correctly. In a nutshell, the process is as follows:

  • an array of data is received from the client
  • it is transformed to an object using Property Mapping
  • this object is validated using the base validators
  • if there is a property mapping or validation error, the last page (which usually contains an edit-form) is re-displayed, an error message is shown and the erroneous field is highlighted.


If you want to suppress the re-display of the last page (which is handled through errorAction(), you can add a @Flow\IgnoreValidation("$comment") annotation to the docblock of the corresponding controller action.

Normally, you build up your Controller with separate actions for displaying a form to edit an entity and another action to actually create/remove/update the entity. For those actions the validation for Domain Model arguments is triggered as explained above. So in order for the automatic re-display of the previous edit form to work, the validation inside that action needs to be suppressed, or else it would itself possibly fail the validation and try to redirect to previous action, ending up in an infinite loop.

class CommentController extends NeosFlowMvcControllerActionController {

  • @param YourPackageDomainModelComment $comment
  • @FlowIgnoreValidation(“$comment”)


public function editAction(YourPackageDomainModelComment $comment) {
// here, $comment is not necessarily a valid object


  • @param YourPackageDomainModelComment $comment


public function updateAction(YourPackageDomainModelComment $comment) {
// here, $comment is a valid object




You should always annotate the model arguments of your form displaying actions to ignore validation, or else you might end up with an infinite loop on failing validation.

Furthermore, it is also possible to execute additional validators only for specific action arguments using @Flow\Validate inside a controller action:

class CommentController extends \Neos\Flow\Mvc\Controller\ActionController {

         * @param \YourPackage\Domain\Model\Comment $comment
         * @Flow\Validate(argumentName="comment", type="YourPackage:SomeSpecialValidator")
        public function updateAction(\YourPackage\Domain\Model\Comment $comment) {
                // here, $comment is a valid object


It is also possible to add an additional validator for a sub object of the argument, using the “dot-notation”: @Flow\Validate(argumentName="comment.text", type="....").

However, it is a rather rare use-case that a validation rule needs to be defined only in the controller.

Using Validators & The ValidatorResolver

A validator is a PHP class being responsible for checking validity of a certain object or simple type.

All validators implement \Neos\Flow\Validation\Validator\ValidatorInterface, and the API of every validator is demonstrated in the following code example:

        // NOTE: you should always use the ValidatorResolver to create new
        // validators, as it is demonstrated in the next section.
$validator = new \Neos\Flow\Validation\Validator\StringLengthValidator(array(
        'minimum' => 10,
        'maximum' => 20

        // $result is of type Neos\Error\Messages\Result
$result = $validator->validate('myExampleString');
$result->hasErrors(); // is FALSE, as the string is longer than 10 characters.

$result = $validator->validate('short');
$result->hasErrors(); // is TRUE, as the string is too short.
$result->getFirstError()->getMessage(); // contains the human-readable error message

On the above example, it can be seen that validators can be re-used for different input. Furthermore, a validator does not only just return TRUE or FALSE, but instead returns a Result object which you can ask whether any errors happened. Please see the API for a detailed description.


The Neos\Error\Messages\Result object has been introduced in order to make more structured error output possible – which is especially needed when objects with sub-properties should be validated recursively.

Creating Validator Instances: The ValidatorResolver

As validators can be both singleton or prototype objects (depending if they have internal state), you should not instantiate them directly as it has been done in the above example. Instead, you should use the \Neos\Flow\Validation\ValidatorResolver singleton to get a new instance of a certain validator:

$validatorResolver->createValidator($validatorType, array $validatorOptions);

$validatorType can be one of the following:

  • a fully-qualified class name to a validator, like Your\Package\Validation\Validator\FooValidator

  • If you stick to the <PackageKey>\Validation\Validator\<ValidatorName>Validator convention, you can also fetch the above validator using Your.Package:Foo as $validatorType.

    This is the recommended way for custom validators.

  • For the standard validators inside the Neos.Flow package, you can leave out the package key, so you can use EmailAddress to fetch Neos\Flow\Validation\Validator\EmailAddressValidator

The $validatorOptions parameter is an associative array of validator options. See the validator reference in the appendix for the configuration options of the built-in validators.

Default Validators

Flow is shipped with a big list of validators which are ready to use – see the appendix for the full list. Here, we just want to highlight some more special validators.

Additional to the simple validators for strings, numbers and other basic types, Flow has a few powerful validators shipped:

  • GenericObjectValidator validates an object by validating all of its properties. This validator is often used internally, but will rarely be used directly.
  • CollectionValidator validates a collection of objects. This validator is often used internally, but will rarely be used directly.
  • ConjunctionValidator and DisjunctionValidator implement logical AND / OR conditions.

Furthermore, almost all validators of simple types regard NULL and the empty string ('') as valid. The only exception is the NotEmpty validator, which disallows both NULL and empty string. This means if you want to validate that a property is e.g. an email address and does exist, you need to combine the two validators using a ConjunctionValidator:

$conjunctionValidator = $validatorResolver->createValidator('Conjunction');

Validating Domain Models

It is very common that a full Domain Model should be validated instead of only a simple type. To make this use-case more easy, the ValidatorResolver has a method getBaseValidatorConjunction which returns a fully-configured validator for an arbitrary Domain Object:

$commentValidator = $validatorResolver->getBaseValidatorConjunction('YourPackage\Domain\Model\Comment');
$result = $commentValidator->validate($comment);

The returned validator checks the following things:

  • All property validation rules configured through @Flow\Validate annotations on properties of the model:

    namespace YourPackage\Domain\Model;
    use Neos\Flow\Annotations as Flow;
    class Comment {
             * @Flow\Validate(type="NotEmpty")
            protected $text;
            // Add getters and setters here

    It also correctly builds up validators for Collections or arrays, if they are properly typed (Doctrine\Common\Collection<YourPackage\Domain\Model\Author>).

  • In addition to validating the individual properties on the model, it checks whether a designated Domain Model Validator exists; i.e. for the Domain Model YourPackage\Domain\Model\Comment it is checked whether YourPackage\Domain\Validator\CommentValidator exists. If it exists, it is automatically called on validation.

When specifying a Domain Model as an argument of a controller action, all the above validations will be automatically executed. This is explained in detail in the following section.

Validation on Aggregates

In Domain Driven Design, the Aggregate is to be considered a consistency boundary, meaning that the whole Aggregate needs to preserve it’s invariants at all times. For that reason, validation inside an Aggregate will cascade into all entities and force relations to be loaded. So if you have designed large Aggregates with a deep hierarchy of many n-ToMany relations, validation can easily become a performance bottleneck.

It is therefore, but not limited to this reason, highly recommended to keep your Aggregates small. The validation will stop at an Aggregate Root, if the relation to it is lazy and not yet loaded. Entity relations are lazy by default, and as long as you don’t also submit parts of the related Aggregate, it will not get loaded before the validation kicks in.


Be careful though, that loading the related Aggregate in your Controller will still make it get validated during persistence. That is another good reason why you should try to minimize relations between Aggregates and if possible, try to stick to a simple identifier instead of an object relation.

For a good read on designing Aggregates, you are highly encouraged to take a read on Vaughn Vernon’s essay series Effective Aggregate Design.

Advanced Feature: Partial Validation

If you only want to validate parts of your objects, f.e. want to store incomplete objects in the database, you can assign special Validation Groups to your validators.

It is possible to specify a list of validation groups at each @Flow\Validate annotation, if none is specified the validation group Default is assigned to the validator.

When invoking validation, f.e. in the MVC layer or in persistence, only validators with certain validation groups are executed:

  • In MVC, the validation group Default and Controller is used.
  • In persistence, the validation group Default and Persistence is used.

Additionally, it is possible to specify a list of validation groups at each controller action via the @Flow\ValidationGroups annotation. This way, you can override the default validation groups that are invoked on this action call, for example when you need to validate uniqueness of a property like an e-mail adress only in your createAction.

A validator is only executed if at least one validation group overlap.

The following example demonstrates this:

class Comment {
         * @Flow\Validate(type="NotEmpty")
        protected $prop1;

         * @Flow\Validate(type="NotEmpty", validationGroups={"Default"})
        protected $prop2;

         * @Flow\Validate(type="NotEmpty", validationGroups={"Persistence"})
        protected $prop3;

         * @Flow\Validate(type="NotEmpty", validationGroups={"Controller"})
        protected $prop4;

         * @Flow\Validate(type="NotEmpty", validationGroups={"createAction"})
        protected $prop5;

class CommentController extends \Neos\Flow\Mvc\Controller\ActionController {

         * @param Comment $comment
         * @Flow\ValidationGroups({"createAction"})
        public function createAction(Comment $comment) {
  • validation for prop1 and prop2 are the same, as the “Default” validation group is added if none is specified
  • validation for prop1 and prop2 are executed both on persisting and inside the controller
  • validation for $prop3 is only executed in persistence, but not in controller
  • validation for $prop4 is only executed in controller, but not in persistence
  • validation for $prop5 is only executed in createAction, but not in persistence

If interacting with the ValidatorResolver directly, the to-be-used validation groups can be specified as the last argument of getBaseValidatorConjunction().

Avoiding Duplicate Validation and Recursion

Unlike simple types, objects (or collections) may reference other objects, potentially leading to recursion during the validation and multiple validation of the same instance.

To avoid this the GenericObjectValidator as well as anything extending AbstractCompositeValidator keep track of instances that have already been validated. The container to keep track of these instances can be (re-)set using setValidatedInstancesContainer defined in the ObjectValidatorInterface.

Flow resets this container before doing validation automatically. If you use validation directly in your controller, you should reset the container directly before validation, after any changes have been done.

When implementing your own validators (see below), you need to pass the container around and check instances against it. See AbstractCompositeValidator and isValidatedAlready in the GenericObjectValidator for examples of how to do this.

Writing Validators

Usually, when writing your own validator, you will not directly implement ValidatorInterface, but rather subclass AbstractValidator. You only need to specify any options your validator might use and implement the isValid() method then:

 * A validator for checking items against foos.
class MySpecialValidator extends \Neos\Flow\Validation\Validator\AbstractValidator {

         * @var array
        protected $supportedOptions = array(
                'foo' => array(NULL, 'The foo value to accept as valid', 'mixed', TRUE)

         * Check if the given value is a valid foo item. What constitutes a valid foo
         is determined through the 'foo' option.
         * @param mixed $value
         * @return void
        protected function isValid($value) {
                if (!isset($this->options['foo'])) {
                        throw new \Neos\Flow\Validation\Exception\InvalidValidationOptionsException(
                                'The option "foo" for this validator needs to be specified', 12346788

                if ($value !== $this->options['foo']) {
                        $this->addError('The value must be equal to "%s"', 435346321, array($this->options['foo']));

In the above example, the isValid() method has been implemented, and the parameter $value is the data we want to check for validity. In case the data is valid, nothing needs to be done.

In case the data is invalid, $this->addError() should be used to add an error message, an error code (which should be the unix timestamp of the current time) and optional arguments which are inserted into the error message.

The options of the validator can be accessed in the associative array $this->options. The options must be declared as shown above. The $supportedOptions array is indexed by option name and each value is an array with the following numerically indexed elements:

# default value of the option # description of the option (used for documentation rendering) # type of the option (used for documentation rendering) # required option flag (optional, defaults to FALSE)

The default values are set in the constructor of the abstract validators provided with FLOW3. If the required flag is set, missing options will cause an InvalidValidationOptionsException to be thrown when the validator is instantiated.

In case you do further checks on the options and any of them is invalid, an InvalidValidationOptionsException should be thrown as well.


Because you extended AbstractValidator in the above example, NULL and empty string are automatically regarded as valid values; as it is the case for all other validators. If you do not want to accept empty values, you need to set the class property $acceptsEmptyValues to FALSE.