How to change entity before it is created or updated.

How to change entity before it is created or updated.

Example How to change entity before it is created or updated using hook_entity_presave().

function MODULE_entity_presave(EntityInterface $entity)
{
    if ($entity->getEntityTypeId() == 'node') {
        if ($entity->getType() == 'article') {
            $entity->set('title', $title);
        }
    }
}

Example 2:

/**
 * Implements hook_entity_presave().
 */
function YOUR_MODULE_entity_presave(Drupal\Core\Entity\EntityInterface $entity) {
  switch ($entity->bundle()) {
    // Here you modify only your day content type
    case 'day':
      // Setting the title with the value of field_date.
      $entity->setTitle($entity->get('field_date')->value);
     break;
  }
}