So let me see if I get this straight. The CustomConstraintValidatorServiceProvider would look like this:

```php
$app['validator.unique'] = $app->share(function ($app) {
    return new UniqueValidator($app['db']);
});
```

And the custom `Unique` constraint would look like this:

```php
public function validatedBy()
{
    return 'exists_validator_alias';
}
```

So that we then register `ValidatorServiceProvider`:

```php
$app->register(new ValidatorServiceProvider(), array(
    'validator.validator_service_ids' => array(
        'exists_validator_alias' => 'validator.exists' // or flipped? not sure.
    )
));
```

So that the ConstraintValidatorFactory would look for `$this->validators['exists_validator_alias']` which would result in `validator.exists` so that we can instantiate it using $this->container['validator.exists'].

Correct?