I have a custom entity (Possession) which has a non-standard edit form. The route for the edit form is the following.

entity.possession.edit: path: '/individual/{individual}/possession/{possession}/edit' defaults:   _entity_form: 'possession.edit'   _title: 'Edit Possession' requirements:   _permission: 'access administration pages' options:   _admin_route: FALSE    parameters:     individual:       type: entity:individual     possession:       type: entity:possession 

That seems to work fine. Instead, the delete form doesn’t work. When I click on delete, I get the following exception.

SymfonyComponentRoutingExceptionMissingMandatoryParametersException: Some mandatory parameters are missing ("individual") to generate a URL for route "entity.possession.edit_form". in DrupalCoreRoutingUrlGenerator->doGenerate() (line 182 of core/lib/Drupal/Core/Routing/UrlGenerator.php).

After a little bit of digging, I noticed that the cancel link on the delete form redirects users to the edit form, which needs those parameters. I ran into this problem with the List Builder page, but I just fixed it in the code for that page.

I tried to edit the PossessionDeleteForm.php file that was generated from Drupal Console. I added a buildForm() method.

public function buildForm(array $form, FormStateInterface $form_state) {   $form = parent::buildForm($form, $form_state);   $entity = $this->entity;    $form['actions']['cancel']['#url'] =  Url::fromRoute('entity.possession.edit_form', [   'possession' => $entity->id(),   'individual' => $entity->get('individual_id')->target_id,   ]);     return $form;  } 

If I use ksm() to inspect the form, it seems it’s setup correctly, but it doesn’t change the thrown exception. I also tried adding the getCancelURL() method to the class with a basic URL, but it didn’t fix the error.

public function getCancelURL() {   return new Url('system.admin_content'); } 

Next I tried the urlRouteParamters() method in the entity class.

protected function urlRouteParameters($rel) {   $uri_route_parameters = parent::urlRouteParameters($rel);       if ($rel === 'edit_form') {        $uri_route_parameters['individual'] = $this->get('individual_id')->target_id;   }    return $uri_route_parameters; } 

That also didn’t work. I have no idea what else to do here.

What is the correct way to redirect users to the edit form, when deleting the entity is cancelled?