nerdfisch: DevBits

  field_media:
    - plugin: merge
      source:
        - field_image
        - field_images
    - plugin: sub_process
      process:
        target_id:
          - plugin: migration_lookup
            source: fid
            migration:
              - my_migration_media_image

<?php

/**
 * Update node title of all nodes.
 */
function custom_module_update_10001(&$sandbox) {
  // Define you entity type.
  $entity_type = 'node';

  // Load the entity type manager service.
  $entity_type_manager = \Drupal::service('entity_type.manager');

  // Get the storage for the entity type.
  $entity_storage = $entity_type_manager->getStorage($entity_type);

  if (!isset($sandbox['total'])) {
    $all_entity_ids = $entity_storage->getQuery()
      ->accessCheck()
      ->execute();
    $sandbox['total'] = count($all_entity_ids);
    $sandbox['current'] = 0;

    if (empty($sandbox['total'])) {
      $sandbox['#finished'] = 1;
      return;
    }
  }

  $entities_per_batch = 25;
  $entity_ids = $entity_storage->getQuery()
    ->accessCheck()
    ->range($sandbox['current'], $entities_per_batch)
    ->execute();
  if (empty($entity_ids)) {
    $sandbox['#finished'] = 1;
    return;
  }

  // Optionally, perform operations with the loaded entities.
  // For example, load and modify each node and set a new title.
  foreach ($entity_ids as $entity_id) {
    $entity = $entity_storage->load($entity_id);

    if ($entity->hasField('title')) {
      $entity->setTitle('New Title');
    }

    $entity->save();
    $sandbox['current']++;
  }

  \Drupal::messenger()
    ->addMessage($sandbox['current'] . ' users processed.');

  if ($sandbox['current'] >= $sandbox['total']) {
    $sandbox['#finished'] = 1;
  }
  else {
    $sandbox['#finished'] = ($sandbox['current'] / $sandbox['total']);
  }

}

/**
 * Run missing database schema updates.
 */
function mymodule_update_10001(&$sandbox) {
  $entity_type_manager = \Drupal::entityTypeManager();
  $entity_type_manager->clearCachedDefinitions();
  $change_summary = \Drupal::service('entity.definition_update_manager')->getChangeSummary();
  foreach ($change_summary as $entity_type_id => $change_list) {
    $entity_type = $entity_type_manager->getDefinition($entity_type_id);
    \Drupal::entityDefinitionUpdateManager()->installEntityType($entity_type);
  }
}

<?php

use Drupal\views\Plugin\Block\ViewsBlock;

/**
 * Implements hook_block_alter().
 */
function hook_block_alter(array &$definitions) {
  foreach ($definitions as $block_id => &$block_definition) {
    if ($block_definition['class'] === ViewsBlock::class) {
      $block_definition['class'] = 'Drupal\my_module\Plugin\Block\ViewsBlock';
    }
  }
}

<?php

namespace Drupal\my_module\Plugin\Block;

use Drupal\views\Plugin\Block\ViewsBlock as ViewsBlockCore;

/**
 * Replaces the generic Views block.
 */
class ViewsBlock extends ViewsBlockCore {

  /**
   * {@inheritdoc}
   */
  public function build() {
    if (empty($this->view->result) && empty($this->view->empty)) {
      // Without caching.
      // return ['#cache' => ['max-age' => 0]];
      // With hard caching.
      return [];
    }

    return parent::build();
  }

}