How can I programmatically delete a field value?

Question

Using Entity API, I know how to get a value or to set a value :

$nid = $entity->id();
$node = \Drupal::entityTypeManager()->getStorage('node')->load($nid);
...
$nom = strtoupper($node->get('field_nom')->value);
$node->set('field_nom', $nom);
$node->save();

But is there a possibility to delete a value of this field?

I tried to directly delete the value in the database

$query =\Drupal::database()->delete('node__field_nom');
$query->condition('field_nom', $nom);
$query->execute();

But since the value is cached, the node have to reload twice to see the result on the screen (an empty field)

Answer 1

The field content is a field item list and normally you would need to include a single value also in an array. The fact that you can set a scalar like in your example is due to extra code in the Field API detecting the scalar and transferring it to a field item list with a single value. To delete the field you can't set an empty scalar, though, because this would be interpreted as a single field item with that empty value.

So to delete the entire field content set an empty array:

$node->set('field_nom', []);

---

BTW you can get the entire field content:

$values = $node->get('field_nom')->getValue();

Change the array $values and set it again:

$node->set('field_nom', $values);