Programmatically update a field's value

Question

I want to update a node field's value when a node is updated.

Tried using the code mentioned here Programmatically updating a node Drupal 8

use Drupal\node\Entity\Node;

    function hello_world_entity_presave(Drupal\Core\Entity\EntityInterface $entity) {

      $check = \Drupal::routeMatch()->getParameter('node');

      if ($check) {
      $node = Node::load($check->nid->value);
      $node->title->value = 'testing';     //set value for field
      $node->save();
      }
    }

but it did not work. I get a 500 error after saving the node. I also tried taking out the if statement and specifying a node id $node = Node::load(1);

I also tried using Update a node / Entity programmatically in Drupal 8

use Drupal\node\Entity\Node;


function hello_world_node_update(Drupal\node\NodeInterface $node) {

$node = Node::load(1);
$node->set("title", 'New value'); // also tried $node->setTitle('The new Title');
$node->save();

}

but no luck either.

In addition, I tried using different hooks entity_presave, entity_update, node_update, but did not make any difference.

Answer 1

You can try this code:

function MODULE_NAME_node_presave(Drupal\node\NodeInterface $node) {
  $node->setTitle('new Title');
  $node->set('body', 'this is body');
}

Answer 2

This is another variation with using the hook you originally tried to use.

I think the problem with your code is that you try to load a new instance of the node, but you should use the node that is provided as paramater $entity:

use Drupal\node\NodeInterface;

function hello_world_entity_presave(Drupal\Core\Entity\EntityInterface $entity)   {
  if ($entity instanceof NodeInterface) {
    $entity->title->value = 'testing';     //set value for field
    // $entity->save(); (not needed)
  }
}

Edit:

Added the use statement to the code.

Answer 3

Titles in Drupal 8 are not set like standard fields; they have their own function. Use $node->setTitle('New Title'); for a node or $entity->setLabel('New Title'); for a generic entity. See Node::setTitle for more info.