Custom Validator

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Here's the situation: all authenticated users should have access to create a CheeseListing... and one of the fields that can be passed is owner. But the data passed to the owner field may be valid or invalid depending on who you're authenticated as. For a normal user, I'm supposed to set this to my own IRI: if I try to set it to a different IRI, that should be denied. But for an admin user, they should be allowed to set the IRI to anyone.

When the value of a field may be allowed or not allowed based on who is authenticated, that should be protected via validation... which is why we're expecting a 400 status code - not a 403.

Generating the Custom Validator

Ok, so how can we make sure the owner field is set to the currently-authenticated user? Via a custom validator. Find your terminal and kick things off with:

php bin/console make:validator

Call it IsValidOwner. If you're not familiar with validators, each validation constraint consists of two classes - you can see them both inside the src/Validator/ directory. The first class represents the annotation that we will use to activate this... and it's usually empty, except for a few properties that are typically public. Each public property will become an option that you can pass to the annotation. More on that in a minute.

... lines 1 - 9
class IsValidOwner extends Constraint
{
/*
* Any public properties become valid options for the annotation.
* Then, use these in your validator class.
*/
public $message = 'The value "{{ value }}" is not valid.';
}

The other class, which typically has the same name plus the word "Validator", is what will be called to do the actual work of validation. The validation system will pass us the $value that we're validating and then we can do whatever business logic we need to determine if it's valid or not. If the value is invalid, you can use this cool buildViolation() thing to set an error.

... lines 1 - 7
class IsValidOwnerValidator extends ConstraintValidator
{
public function validate($value, Constraint $constraint)
{
/* @var $constraint \App\Validator\IsValidOwner */
if (null === $value || '' === $value) {
return;
}
// TODO: implement the validation here
$this->context->buildViolation($constraint->message)
->setParameter('{{ value }}', $value)
->addViolation();
}
}

Using the Validation Constraint

To see this in practice, open up CheeseListing. The property that we need to validate is $owner: we want to make sure that it is set to a "valid" owner... based on whatever crazy logic we want. To activate the new validator, add @IsValidOwner(). This is where we could customize the message option... or any public properties we decide to put on the annotation class.

... lines 1 - 10
use App\Validator\IsValidOwner;
... lines 12 - 48
class CheeseListing
{
... lines 51 - 95
/**
... lines 97 - 99
* @IsValidOwner()
*/
private $owner;
... lines 103 - 206
}

Actually, let's change the default value for $message:

Cannot set owner to a different user

... lines 1 - 9
class IsValidOwner extends Constraint
{
... lines 12 - 15
public $message = 'Cannot set owner to a different user';
}

Ok, now that we've added this annotation, whenever the CheeseListing object is being validated, the validation system will now call validate() on IsValidOwnerValidator. The $value will be the value of the $owner property. So, a User object. It also passes us $constraint, which will be an instance of the IsValidOwner class where the public properties are populated with any options that we may have passed to the annotation.

Avoid Validating Empty Values

The first thing the validator does is interesting... it checks to see if the $value is, sort of, empty - if it's null. If it is null, instead of adding a validation error, it does the opposite! It returns.. which means that, as far as this validator is concerned, the value is valid. Why? The philosophy is that, if you want this field to be required, you should add an additional annotation to the property - the @Assert\NotBlank constraint. We'll do that a bit later. That means that our validator only has to do its job if there is a value set.

The setParameter() Wildcard

To see if this is working... ah, let's just try it! Sure, we haven't added any logic yet... and so this constraint will always have an error... but let's make sure we at least see that error!

Oh, and this setParameter() thing is a way for you to add "wildcards" to the message. Like, if you set {{ value }} to the email of the User object, you could reference that dynamically in your message with that same {{ value }}. We don't need that... so let's remove it. Oh, and just to be totally clear, the $constraint->message part is referencing the $message property on the annotation class. So, we should see our customized error.

Let's try it! Go tests go!

php bin/phpunit --filter=testCreateCheeseListing

If we scroll up... awesome! It's failing: it's getting back a 400 bad request with:

Cannot set owner to different user

Hey! That's our validation message! The failure comes from CheeseListingResourceTest line 44. Once we use a valid owner IRI, validation still fails because... of course... right now our new validator always adds a violation.

Let's fix that next: let's add real logic to make sure the $owner is set to the currently-authenticated user. Then we'll go further and allow admin users to set the $owner to anyone.

Leave a comment!

  • 2019-09-12 Diego Aguiar

    Proximamente! Este curso esta siendo publicado diariamente

    Saludos!

  • 2019-09-12 Alberto

    Tengo muchas ganas de ver este capítulo!!!