Handles rendering entity validation errors and other exceptions for your API

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v2.0.3 2024-02-17 22:15 UTC


MixerAPI ExceptionRender

Latest Version on Packagist Build Coverage Status MixerApi CakePHP Minimum PHP Version

This plugin handles rendering entity validation errors and other exceptions for your API.

  • Integrates with Validator on add() and edit() actions.
  • Adds the short name of the Exception thrown to the response

Read more at MixerAPI.com.


!!! tip "" You can skip this step if you have MixerApi installed.

composer require mixerapi/exception-render
bin/cake plugin load MixerApi/ExceptionRender

Alternatively after composer installing you can manually load the plugin in your Application:

# src/Application.php
public function bootstrap(): void
    // other logic...


In your config/app.php file change the default exceptionRenderer:

'Error' => [
    'errorLevel' => E_ALL,
    'exceptionRenderer' => MixerApi\ExceptionRender\MixerApiExceptionRenderer::class,
    'skipLog' => [],
    'log' => true,
    'trace' => true,


Define your Validations as normal in your Table classes and MixerApiExceptionRenderer handles the rest by attaching a listener to the afterMarshall event which fires when request data is merged into entities during patchEntity() or newEntity() calls. If a validation fails then a ValidationException is thrown and rendered with an HTTP 422 status code.

Example controller action:

public function add()
    $actor = $this->Actors->newEmptyEntity();
    $actor = $this->Actors->patchEntity($actor, $this->request->getData()); // potential ValidationException here
    if ($this->Actors->save($actor)) {
        $this->viewBuilder()->setOption('serialize', 'actor');
        $this->set('actor', $actor);

    throw new \Exception("Record failed to save");


  "exception": "ValidationException",
  "message": "Error saving resource `Actor`",
  "url": "/actors",
  "code": 422,
  "violations": [
      "propertyPath": "first_name",
      "messages": [
          "rule": "_required",
          "message": "This field is required"
      "propertyPath": "last_name",
      "messages": [
          "rule": "_required",
          "message": "This field is required"

Using the controller example from above, we can catch the exception if desired and perform additional logic:

try {
    $actor = $this->Actors->newEmptyEntity();
    $actor = $this->Actors->patchEntity($actor, $this->request->getData());
} catch (\MixerApi\ExceptionRender\ValidationException $e) {
    // do something here


For non-validation based exceptions, even your projects own custom exceptions, the output is similar to CakePHP native output with the addition of an exception attribute. For example, a MethodNotAllowedException would result in:

  "exception": "MethodNotAllowedException",
  "message": "Your exception message here",
  "url": "/actors",
  "code": 405

If for instance you have a custom exception that is thrown, such as InventoryExceededException, you would see:

  "exception": "InventoryExceededException",
  "message": "No inventory exists",
  "url": "/requested-url",
  "code": 500

Providing an Exception name, in conjunction with the status code already provided by CakePHP, enables API clients to tailor their exception handling.

Disabling ValidationExceptions

There may be times when you don't want ValidationExceptions to run. You can easily disable the event:

Configure::write('MixerApi.ExceptionRender.entity_validation', false);

Another example is you may only want the event to run for non-CLI portions of your application:

Configure::write('MixerApi.ExceptionRender.entity_validation', PHP_SAPI !== 'cli');

Changing Error Messages

ExceptionRender dispatches a MixerApi.ExceptionRender.beforeRender event that you can listen for to alter viewVars and serialize variables. Both are accessible via the MixerApi\ExceptionRender\ErrorDecorator.



namespace App\Event;

use Cake\Event\EventListenerInterface;
use MixerApi\ExceptionRender\ErrorDecorator;
use MixerApi\ExceptionRender\MixerApiExceptionRenderer;

class ExceptionRender implements EventListenerInterface
    public function implementedEvents(): array
        return [
            'MixerApi.ExceptionRender.beforeRender' => 'beforeRender'

     * @param \Cake\Event\Event $event
    public function beforeRender(\Cake\Event\Event $event)
        $errorDecorator = $event->getSubject();
        $data = $event->getData();

        if (!$errorDecorator instanceof ErrorDecorator || !$data['exception'] instanceof MixerApiExceptionRenderer) {

        if (!$data['exception']->getError() instanceof \Authentication\Authenticator\UnauthenticatedException) {

        $viewVars = $errorDecorator->getViewVars();
        $viewVars['message'] = 'A custom unauthenticated message';

Read more about Events in the official CakePHP documentation.