I am using drupal 8 rest and I want to be able to do a few computations and return custom json messages as per the defined condition when posting a user. I am using the already existing /entity/user/ resource provided by core out of the box. I tried to create a custom module and tried to use the Drupal\rest\ResourceResponse class in the module file like below:

function magri_rest_user_presave($account) {

    if (isset($account->field_region->value)) {

        $taxonomy_query = \Drupal::entityQuery('taxonomy_term');
        $taxonomy_query ->condition('vid', "region")
            ->condition('name', $account->field_region->value);
        $tids = $taxonomy_query->execute();

        $tid = array_values($tids)[0];

            //set taxonomy ref field on user entity
            $account->field_region_tax->target_id = $tid;

            $response = ['message' => 'Region not found'];
            return new ResourceResponse($response);

This does not stop the rest call to return the custom message. Is there a way I can archive this withouts creating my own custom rest plugin?

1 Answer 1


You can't return a response from a presave hook. You can however throw an exception, which in a json route will return a json error message:

throw new NotFoundHttpException('Region not found!');

If you want to change the default error response, implement an exception subscriber to catch this exception and return your own response.

For reference the default exception handler: ExceptionJsonSubscriber::on4xx

  • Thank you, but this just throws the exception its not returning a json error message Sep 4, 2019 at 21:11
  • If you have a json route, what I don't know, then Drupal can out-of-the-box return a json error message, as explained in the second part of my answer. In other cases you might need to implement your own exception subscriber.
    – 4uk4
    Sep 5, 2019 at 6:25
  • okay maybe if you point me in the right direction. What is a json route? I am using the rest module, together with REST UI and RESTful Web Services. Sep 5, 2019 at 9:06
  • Add ?_format=json to the requested url.
    – 4uk4
    Sep 5, 2019 at 9:29
  • yet it has. It is actually the only allowed format on all my configured resources. hal_json and xml are disabled. Sep 5, 2019 at 9:36

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