Programmatically Render a Node Edit form with a custom Form Display Mode

Question

I'm attempting to make a page for users to edit data for a specific content type, but I only want them to have access to some of the fields not all. To do so I created a custom form display mode for content. I have a custom controller that is meant to display this form with a custom display mode. Here is the code meant to render it.

    public function showCustomForm() {
        $node = \Drupal::entityTypeManager()->getStorage('node')->load('123');
        $edit_form = \Drupal::entityTypeManager()->getFormObject('node', 'my_custom_form_display_mode_id')->setEntity($node);
        return \Drupal::formBuilder()->getForm($edit_form);
    }

And I get the error

Drupal\Component\Plugin\Exception\InvalidPluginDefinitionException: The "node" entity type did not specify a "my_custom_form_display_mode_id" form class. in Drupal\Core\Entity\EntityTypeManager->getFormObject() (line 184 of /var/www/mydomain/http/web/core/lib/Drupal/Core/Entity/EntityTypeManager.php).

I was using this How do I load a form with a specific form display (form mode)? as an example. But still had no luck.

How would I programmatically load a node edit form with a custom form display mode?

Answer 1

The error message says you did not specify a form class, but what it really wants to say is, that you did not specify a form operation with the name of the form mode:

mymodule.module:

function mymodule_entity_type_build(array &$entity_types) {
  $entity_types['node']->setFormClass('my_custom_form_display_mode_id', 'Drupal\node\NodeForm');
}

The form operation needs a form class. This can be the same as for default, which you find in the handlers section of the annotations in the Node class.