13.11.2025 | Mathias Grab

How to create local task links

my_module.links.task.yml

my_module.my_local_task_link:
  route_name: my_module.custom_route
  title: "Title"
  base_route: route_where.local_task.should_be_placed

Issue:

You want to create a local task link with a specific custom route.

Solution:

To create a local task link, define it in my_module.local.task.yml, optionally accompanied by my_module.routing.yml and MyCustomController.php. Alternatively, you can use existing routes, specifying route_name as the target of the link and base_route as the location where the link should appear.

Explanations for the most important properties in yml files

my.module.links.task.yml

yml property	Description
`my_module.my_local_task_link`	Machine name of the link.
`route_name`	The route the link leads to.
`title`	Human readable title of the link. Is shown on buttons or menu links.
`base_route`	Base route where the link is placed on.

my_module.routing.yml

yml property	Description
`my_module.custom_route`	Machine name of the registered route.
`path`	Path in URL.
`defaults`	Default values for the upcoming properties.
`_controller`	Namespace of the controller that handles the logic when the route is accessed.
`_title`	Human readable title of the route.
`requirements`	Requirements that must be met to access the route.
`_permission`	Permission that must be fulfilled to access the route.

See the official Drupal documentation for further in-depth information.

yml / yaml

local task links

routing

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23.10.2026 | Lothar Ferreira Neumann

How to fill empty form fields via a custom Drupal AJAX command

SetValueIfEmptyCommand.php

<?php

declare(strict_types=1);

namespace Drupal\my_module\Ajax;

use Drupal\Core\Ajax\CommandInterface;

/**
 * Ajax command: fill empty form elements with a predefined value.
 *
 * This command targets one or more form elements via a CSS selector and sets
 * their value only if the current value is empty (after trimming).
 *
 * The command also triggers `input` and `change` events so Drupal behaviors and
 * other listeners react as if the user entered the value manually.
 */
final class SetValueIfEmptyCommand implements CommandInterface {

  /**
   * The Ajax command name used by Drupal.AjaxCommands.
   */
  public const COMMAND = 'setValueIfEmpty';

  /**
   * Default selector used when none is provided.
   */
  public const DEFAULT_SELECTOR = '[data-my-fill-target]';

  /**
   * Creates a command instance.
   *
   * @param string $fillValue
   *   The value to set when the target element is empty.
   * @param string|null $targetSelector
   *   CSS selector for the target elements. If omitted, DEFAULT_SELECTOR is used.
   */
  public function __construct(
    protected string $fillValue,
    protected ?string $targetSelector = null,
  ) {}

  /**
   * {@inheritdoc}
   */
  public function render(): array {
    return [
      'command' => self::COMMAND,
      'selector' => $this->targetSelector ?? self::DEFAULT_SELECTOR,
      'value' => $this->fillValue,
    ];
  }

}

media_fill_if_empty.js

/**
 * @file Field empty check.
 */
(function (Drupal) {
  'use strict';

  Drupal.AjaxCommands.prototype.setValueIfEmpty = function (ajax, response) {
    const targetSelector = response && response.selector ? response.selector : '';
    const fillValue = response && typeof response.value === 'string' ? response.value : '';

    if (!targetSelector) {
      return;
    }

    const elements = document.querySelectorAll(targetSelector);
    for (const element of elements) {
      let currentValue = '';

      if (typeof element.value === 'string') {
        currentValue = element.value.trim();
      }
      else if (element.isContentEditable) {
        currentValue = (element.textContent || '').trim();
      }

      if (currentValue !== '') {
        continue;
      }

      if (typeof element.value === 'string') {
        element.value = fillValue;
      }
      else if (element.isContentEditable) {
        element.textContent = fillValue;
      }
      else {
        continue;
      }

      element.dispatchEvent(new Event('input', { bubbles: true }));
      element.dispatchEvent(new Event('change', { bubbles: true }));
    }
  };

})(Drupal);

my_module.libraries.yml

set_value_if_empty:
  js:
    js/set_value_if_empty.js: {}
  dependencies:
    - core/drupal
    - core/drupal.ajax

MyResponse.php

use Drupal\Core\Ajax\AjaxResponse;
use Drupal\my_module\Ajax\SetValueIfEmptyCommand;

$response = new AjaxResponse();

// Example: fill a media name field if it's empty.
$fill_value = 'foo-bar';

// Selector for a specific element in this use-case.
$target_selector = '[data-drupal-selector$="my_field"]';

$response->addAttachments([
  'library' => [
    'my_module/set_value_if_empty',
  ],
]);

$response->addCommand(new SetValueIfEmptyCommand($fill_value, $target_selector));

return $response;

php

yml / yaml

media

ajax

field values

13.11.2025 | Peter Majmesku

Autowire services with the Autowire attribute in Drupal

Example.php

<?php

declare(strict_types=1);

namespace Drupal\my_module;

use Drupal\Core\Session\AccountInterface;
use Symfony\Component\DependencyInjection\Attribute\Autowire;

class Example {

  public function __construct(
    #[Autowire(service: 'current_user')]
    private readonly AccountInterface $currentUser,
  ) {
  }

  public function getCurrentUser(): AccountInterface {
    return $this->currentUser;
  }

}

my_module.services.yml

services:
  my_module.example:
    class: Drupal\my_module\Service\Example
    autowire: true
  Drupal\my_module\Service\Example: '@my_module.example'

php

services

yml / yaml