Question

When validating a domain entity, is it better to validate the values as they are set, or all at once with a validator (such as in Symfony2) later on?

For example:

Option 1. Validate while being set

public function setEmail($email)
{
    if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        throw new EntityException('The specified email address ' . $email . ' is invalid.');
    }

    $this->_email = $email;
    return $this;
}

Option 2. Validate later…

$user = new UserEntity();
$user->setEmail('[e-mail]');
$validator = new Validator();
$validator->validate($user);

Option 3. Both of the above (although seems a little redundant and not worth the overhead).

I know that the first one probably makes for more airtight entities, but the second one makes for more user friendly error handling.

Also, the second option seems easier to configure and maintain…as I don’t have to adjust the setters, and I can centralize my validation logic to a single class.

What it boils down to…
So basically, it sounds like Option 2 is what I WANT to do, but feel like sacrificing the airtight-ness of the entity (for example, if I forget to run the entity through the validator), might be stupid.

Answer 1

Single Responsibility Principle

The best is to have all necessary validations in a separated layer. With that will be easier to maintain and test the validators. Also easier to validate data across your application.

Don’t Repeat Yourself

You don’t have to call validate() for each entity.

All you have to do is to implement the validation on your repository layer or service layer if you have one.

$user = new User();
// [...]
$user->setEmail('myinvalidemail#blah,com');
$repository->save($user);

So in your user’s repository

UserRepository extends AbstractRepository {}

And the common validation for all entities:

abstract class AbstractRepository {
    public function save($entity) {
        $validator = // Get your validator based on the entity's name or something else
        $validator->validate($entity); // Throws exceptions or flag the  fields for future use

         // Now save it...
    }
}