drupal_8_cheat_sheet.php

<?php

//******** user ***************//

  $current_user = \Drupal::currentUser();
  $current_user_id \Drupal::currentUser()->id();
  $user = User::load($user_id);


//******** messenger - set messeges ***************//

// Messenger - (D7 drupal_set_message)
 \Drupal::messenger()->addMessage(t('Show this message to the user.'));

// Message Types
 \Drupal::messenger()->addMessage($message, 'status');
 \Drupal::messenger()->addMessage($message, 'warning');
 \Drupal::messenger()->addMessage($message, 'error'); 

// Another way of displaying error type messages.
\Drupal::messenger()->addError(t('The user account %id does not exist.', ['%id' => $uid]));

// Using t()
$text = t('My name is %name.<br>My age is %age.', ['%name' => $name, %age -> $age]);


// Formated Array messege
  $formatted_array = print_r($array_data, TRUE);
  $msg = t('Output array data: <pre>@data</pre>', ['@data' => $formatted_array]);
  \Drupal::messenger()->addStatus(['#markup' => $msg]);

// HTML mutly line messege
  $msg = t('<h2>Formatted message</h2><strong>Multi line output</strong><br>Line 1<br>Line 2');
  \Drupal::messenger()->addStatus(['#markup' => $msg]);




// Add messenger to your class for use with $this->messenger
  /**
   * Gets the messenger.
   *
   * @return \Drupal\Core\Messenger\MessengerInterface
   *   The messenger.
   */
  public function messenger() {
    if (!isset($this->messenger)) {
      $this->messenger = \Drupal::messenger();
    }
    return $this->messenger;
  }



// **** working with nodes ****** 

 // Check if an entity is a node.
 if ($entity instanceof \Drupal\node\NodeInterface) {
    $node = $entity;
 }
 // or
 if ($entity->getEntityTypeId() == 'node') {
    $node = $entity;
 }
 
// check the bundle type of a node
$node_type = $entity->getType();

  // Load by ID
  use Drupal\node\Entity\Node; // Add to use section
  $node = Node::load($nid);

   
   //Load mathod 2 - https://www.metaltoad.com/blog/drupal-8-entity-api-cheat-sheet
  $node_storage = \Drupal::entityTypeManager()->getStorage('node');
  $node = $node_storage->load($nid);

  // Get a node from a form
  $node = $form_state->getFormObject()->getEntity();
  $is_new = $node->isNew();

  // Get node id.
  $nid = $node->id();

  // Get node title
  $title = $product->getTitle();    // use this 
  $title = $product->title
   
   
  
  // Get the published state.
  $is_published = $node->isPublished();
  // If we have a modaration workflow - we can get the state "Machine name".
  $moderation_state = $node->moderation_state->value;


  // Get a field value array
  $node->get('field_name')->getValue();
  $node->field_name->getValue();

  // Get the 2nd value of a multi value field
  $node->field_name->getValue()[1]['value'];
  // Get the 3nd reference ID of a multi value entity reference field
  $node->field_name->getValue()[2]['target_id'];
  // Count the number of values
  count($node->field_name->getValue())

  // Get a single field value (shortest form)
  $node->field_name->value;


 // Single node entity reference field
  $nid = $node->get('field_contact')->first()->getValue()['target_id'];
  $node = Node::load($nid);
// or  (shortest form)
  $node->field_contact->target_id;


  // Cycle a Entity reference fields 
  foreach ($node->field_po_lines as $reference) {
    $entity_id = $reference->target_id;
    $entity_storage = \Drupal::entityTypeManager()->getStorage('po_line');
    $entity = $entity_storage->load($entity_id);
  }

  // Cycle a Entity reference fields (th long way)
  foreach ($node->field_po_lines as $po_line) {

    /** @var \Drupal\Core\Entity\Plugin\DataType\EntityReference $entityReference */
    $entityReference = $po_line->get('entity');

    /** @var \Drupal\Core\Entity\Plugin\DataType\EntityAdapter $entityAdapter */
    $entityAdapter = $entityReference->getTarget();

    /** @var \Drupal\Core\Entity\EntityInterface $referencedEntity */
    $referencedEntity = $entityAdapter->getValue();
  }

// Get all the referenced entities in one go
 $all__referenced_entities =  $node->get('field_po_lines')->referencedEntities();

// Create node - need to include:
use Drupal\node\Entity\Node;

// Create a node mathod 1a - simple
 $node = Node::create(['type' => 'article', 'title' => 'Sample article API', 'path' => ['alias' => '/sample-article-api']]);
 $node->save();

// Create a node mathod 1b - more details
    $data = [
      'uid'      => $user->id(),
      'name'     => 'admin',
      'type'     => 'article',
      'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
      'title'    => $this->randomMachineName(),
      'body' => 'body text',
      'multivalue_field' => [ ['value' => 'first'], ['value' => 'second'] ]
      'status' => 1,
      'created' => '1435019805',
    ];
    $node = Node::create($data);
    $node->save();

    // Create a node mathod 2 - field by field
    $node = Node::create(['type' => 'article']);
    $node->set('title', 'Title');
    $node->set('field_text', 'My text');
    $node->save();

    // Create a node mathod 3 - field by field
    \Drupal::entityTypeManager()->getStorage('node')->create(['type' => 'article', 'title' => 'Node title']);


    // Seting Fields

    // Title filed
    $node->set('title', 'Title');
    // Text field
    $node->set('field_text', 'My text');
    // Created date in a unix time stamp
    $node->set('created', time());
    // Date fields are text
    $node->set('field_date', date('Y-m-d', time()));
    $node->set('field_datetime', date('Y-m-d\TH:i:s', time()));
    // User
    $po_node->set('field_user', \Drupal::currentUser()->id());
    
    // reference field (two options)
    $node->field_user->target_id = $user_id;            
    $node->field_user->entity = $user;
    // Multiple values
    $node->field_user[] = ['target_id' => $user_id]; 


    $node->save();

  // Populate a multivalue field for a string holding comma delimited values
  $value = '1,2,3,4';
  $value_array = explode(',', $value);
  foreach ($value as $key => $value) {
    $value_array[$key] = ['value' => trim($value)];
  }
  $node->set('multivalue_field', $value_array;
             
             
  // Create custom entities
   /* @var \Drupal\custom_module\Entity\CustomEntity $newentity */
   $newentity = CustomEntity::create();
             

// ***** Multilingual **** //
// Load a node in the current language.
             
    $current_lang_code = \Drupal::languageManager()->getCurrentLanguage()->getId();             
    $node = Node::load($id);
    if ($node->hasTranslation($current_lang_code)) {
      $node = $node->getTranslation($current_lang_code);
    }
             
             
// **** working with ULs ****** //             

  // Get the curent path (will give you the internal path i.e. node/5)
  $internalt_path = \Drupal::service('path.current')->getPath();
             
   // Get the curent path alias will give you the path alias i.e. /the_path/to/a_page)
  $current_path = \Drupal\Core\Url::fromRoute('<current>')->toString();
             
  // Get the path alias from the internal path
  $path_alias = \Drupal::service('path_alias.manager')->getAliasByPath($internalt_path);           

  // Get the path alias of node/5
  $path_alias = \Drupal::service('path_alias.manager')->getAliasByPath('node/5');           
  
  // Get a localised URL for node/5
  $current_lang_code = \Drupal::languageManager()->getCurrentLanguage()->getId();
  // The alias does not contain the language prefex so we need to add it.
  $node_url = "/$current_lang_code" . \Drupal::service('path_alias.manager')->getAliasByPath('/node/5', $current_lang_code);
             
             
             
   // Get the path arguments into an array /arg1/arg2/...          
    $path_args = explode('/', $current_path);
    $arg1 = $path_args[1];  // $path_args[0] - is empty resulting from the leading slash and should be ignored
    $arg2 = $path_args[2];
             
    // Get the query strings: {url}/arg1/arg?p1=123&p2=456
    $p1 = \Drupal::request()->query->get('p1');
    $p2 = \Drupal::request()->query->get('p2');
                          
    // Getting the referer from the request.
    $request = \Drupal::request();
    $referer = $request->headers->get('referer');
    
    // Converting the referer into a request and getting its query strings
    use Symfony\Component\HttpFoundation\Request;
    .....
    $ref_request = Request::create($referer, 'GET');
    $staff_id = $ref_request->query->get('qs1');
    $return_url = $ref_request->query->get('qs2');
    
             
    // Redirect from a form submit
     public function submitForm(array &$form, FormStateInterface $form_state) {
       // uses use Drupal\Core\Url;
        ....             
       $url = Url::fromUserInput('/arg1/arg2/do-it', ['query' => ['qry-string' => $nid]]);
       $form_state->setRedirectUrl($url);
     }
     
   // Redirect from inside a hook (preserving a query string)
      use Symfony\Component\HttpFoundation\RedirectResponse;
      use Drupal\Core\Url;
       ....
     $redirect_url .= '/new_url?' . \Drupal\Component\Utility\UrlHelper::buildQuery(['qs1' => $staff_id]);     
     $redirect = new RedirectResponse($redirect_url);
     $redirect->send();
     

  // Get a URL for a drupal route (views example)
  $url = Url::fromRoute('view.view_name.page_1');
  // Add options (adding a class in this example)
  $link_options = [
    'attributes' => [
      'class' => [
        'btn',
      ],
    ],
  ];
  $url->setOptions($link_options);
  // get the link
  $link = new Link(t('Show All'), $url);
             
             
             
     // Use drupal consol to list all the rout names
     $ drupal router:debug
     
    // Redirect from a Controller (derived from ControllerBase)
    // Add to the uses section: use Drupal\Core\Url; 
    $destination = Url::fromUserInput('/go-somplace-else');
    return $this->redirect($destination->getRouteName());

    // Using Symfony
    use Symfony\Component\HttpFoundation\RedirectResponse;
    
    return new RedirectResponse(Url::fromUserInput('/some-url')->toString());
    return new RedirectResponse(Url::fromRoute('<front>')->toString());
    
             
//******** State API ***************//             
             
// States - Get a state with a defult of FALSE
\Drupal::state()->get('my_state_var_name', FALSE)
             
//******** Cache API ***************//             

  // Cache API data for 24 hours:
  $cid = 'test_module_api_product_data';
  if ($cache = \Drupal::cache()->get($cid)) {
    $products = $cache->data;
  }
  else {
    $products = $this->Api->getProducts();
    // Cache for 24 hours.
    $expire = time() + 24*60*60;
    \Drupal::cache()->set($cid, $products, $expire);
  }
            
  // Using bins           
  $cache = \Drupal::cache()->get($cid)
  // is the same as calling:
  $cache = \Drupal::cache('default')->get($cid)      
  // and will get the data from the cache_default table.
             
  // you can use other bins:
  $cache = \Drupal::cache('data')->get($cid)      
  $cache = \Drupal::cache('entity')->get($cid)      
  $cache = \Drupal::cache('dynamic_page_cache')->get($cid)      
             
  //for custom bins see:
  https://www.hashbangcode.com/article/drupal-8-custom-cache-bins             
             
             
//******** Configuration API ***************//             

    // read a value.         
    $config = \Drupal::config('mymodule.myconfig');
    $config_var = $config->get('var_name');
    // One liner.         
    $config_var = \Drupal::config('mymodule.myconfig')->get('var_name');
             
    // Read a value from a config form and save.         
    $field_value = (int) $form_state->getValue('my_state_field_name');
    \Drupal::config('mymodule.myconfig')
      ->set('var_name', $field_value)
      ->save();

//******** Watchdog ***************//             
             
// Logger/watchdog
    $logger = \Drupal::logger('channel name');  // $channel - The name of the channel Can be any string, but the general practice is to use the name of the subsystem/module calling this.
    $logger->info('log a simple info message');
    $logger->notice('log a simple notice message');
    $logger->warning('log a simple warning message');
    $logger->error('log a simple error message');

    // Argument examples
    $logger->info('Starting execution of @module_cron() job %job_text, execution of @module_previous_cron() took @time.', [
          '@module' => $module,
          '%job_text' => 'some text',  
          '@module_previous' => $module_previous,
          '@time' => Timer::read('cron_' . $module_previous) . 'ms',
        ]);
             
    // Multi lines example:
      $this->logger->info("Import completed in @time seconds.<br>
            Imported: @imported.<br>
            Updated: @updated<br>
            Deleted: @deleted",
        [
          '@time' => $group_run_time,
          '@imported' => $import_count,
          '@updated' => $updated,
          '@deleted' => $deleted,
        ]);
             
             
             
    // @todo - Not sure about this notation.  
    $this->logger->info('Received a payload from client {clientId}', ['clientId' => $clientId]);
             

    // complex use
    $context = [
      'channel' => $type,
    ];
          $error_args = [
            '@api_path' => $api_path,
            '@response_code' => $api_response_code,
            '@response_error' => $api_response_error,
            '@response_data' => print_r($api_response, TRUE)
          ];
          $error_msg = t('Get request failed for @api_path, code: @response_code error: @response_error,
                <pre><code> Response data: @response_data</code></pre>', $error_args);
        }
             
    $logger->error($message, $context);             
             

  // Get the list of options for a list field.
  $e_manager=\Drupal::entityManager();
  $field_definition = $e_manager->getFieldDefinitions("node","person")["field_profession"];
  $profession_allowed_values = $field_definition->getFieldStorageDefinition()->toArray()["settings"]["allowed_values"];
  // Can be used to get the display of the field value
  $profession_id = $node->field_judge_panel->value
  $profession_name = $profession_allowed_values[$profession_id];            
             
             

drupal_exception.php

<?php

// Catch all
   try {
      // Some code
      return TRUE;     
    }
    catch (\Exception $e) {
      $this->logger->error("Code failed with exception: @exception", [
        '@sku' => $part_number,
        '@exception' => $e->getMessage()
      ]);
      return FALSE;
    }
    catch (\Throwable $e) {
      $this->logger->error("Code failed with Throwable exception: @exception", [
        '@sku' => $part_number,
        '@exception' => $e->getMessage()
      ]);
      return FALSE;
    }


// Detailed logg of the exception
    try {
       // ....
    }
    catch (\Exception $e) {
      $logger = \Drupal::logger('my_module_name');
      $logger>error(t('function_name Exception:') . $e->getMessage(), array('exception' => $e));
      return [];
    }

drupal_form_submit_func.php

<?php

//** Patarn 1: Add multiple submits to a config from. **//

  public function buildForm(array $form, FormStateInterface $form_state): array {

  // Array elements
    $form['some_element'] = [
      '#type' => 'some_type',
      ...
    ];    

   // New Submit
    $form['test_submit'] = [
      '#type' => 'submit',
      '#name' => 'run-test',
      '#value' => $this->t('Run test'),
      '#submit' => [ [$this, 'runTest'] ]
    ];
  }

// This will be called if ragulr submit is pressed.
  public function submitForm(array &$form, FormStateInterface $form_state): void {
    \Drupal::messenger()->addMessage('Normal Form Submit', 'status');
    // ... some code.
    parent::submitForm($form, $form_state);
  }

// This will be called if the "Run test" submit is pressed.
  public function runTest(array &$form, FormStateInterface $form_state) {
    \Drupal::messenger()->addMessage('Run Test', 'status');
  }


//** Patarn 2: Add optional submits to a config from. **//


  public function buildForm(array $form, FormStateInterface $form_state): array {

  // Array elements
    $form['some_element'] = [
      '#type' => 'some_type',
      ...
    ];    

   // New Submit
    $form['test_submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Run Test'),
      '#id' => 'run-test',
    ];
  }

  public function submitForm(array &$form, FormStateInterface $form_state): void {
    \Drupal::messenger()->addMessage('Normal Form Submit', 'status');
    // ... some code.
    
    // Optional actions
    $action = $form_state->getTriggeringElement();
    $action_id = $action['#id'];
    if ($action_id == 'run-test') {
      \Drupal::messenger()->addMessage('Run Test', 'status');
    }
    
    parent::submitForm($form, $form_state);
  }

images_and_files.php

<?php
use Drupal\Core\Link;
use Drupal\Core\Url;

// Get the Url object for a node edit form
      $url = Url::fromRoute('entity.node.edit_form', ['node' => $nid]);
      
     // Get an internal URL. 
    $url = Url::fromUri( 'internal:/someplace/on_the_site');
  
    // Convert to link
    $link = new Link('Click me', $url);   
    $link_txt = $link->toString();
      
// URL from URI
         $url = \Drupal::service('file_url_generator')->generateString($uri);   // reletive
         $url = \Drupal::service('file_url_generator')->generateAbsoluteString($uri); // FULL

my_module.theme

<?php

// Set variables for a node template

/*
 * Implements theme_preprocess_node
 *
 */
function my_module_preprocess_node(&$variables) {
  $node = &$variables['node'];
  $view_mode = &$variables['view_mode'];

  $bundle = $node->bundle();
  switch ($bundle) {
    case 'home_page':
      $variables['page'] = 'home';
      break;
    case 'landing_page':
      $variables['page'] = 'landing';
      $variables['display_submitted'] = False;
      break;
    case 'report_page':
      $variables['page'] = 'report';
      $one = $node->field_one->value;
      $variables['one'] = $one;      
      break;
  }
}

in something.template.html.twig
<div>This is a {{ page }} page</div>

node_func.php

<?php

// hook_node_presave() example
// Set the node title to first and last name. 
// You should disable the title in the manage form display.
function my_module_node_presave($node){
  $first_name = $node->field_first_name->value;
  $last_name = $node->field_last_name->value;
  $name = $first_name;
  if (!empty($last_name)) {
    $name .= ' ' .  $last_name;
  }
  $node->set('title', $name);
}

user_fun.php

<?php

// User get and load functions.
  $current_user = \Drupal::currentUser();
  $current_user_id \Drupal::currentUser()->id();
  $user = User::load($user_id);

// Check if a user is logged in / Authenticated.
\Drupal::currentUser()->isAuthenticated()
  
// Check if a user has a role.  
    $current_user = \Drupal::currentUser();
    $user_roles = $current_user->getRoles();
    if (in_array('administrator', $user_roles)) {
      // Do stuff
    }