Is there a hook which could be used to execute code when a specific field of a custom content type is updated? Is there a specific hook, or should I use hook_node_presave()? In that case, how could I check that the field's value has indeed been modified?

  • I think I know what you are going for - might want to check the answers here first. drupal.stackexchange.com/questions/183477/… – Kevin Jan 14 '17 at 17:58
  • @Kevin thank you very much for your time. However, this question does not refer to creating a new node. It refers on updating a node's field. – Pantelis Natsiavas Jan 14 '17 at 18:05

Using hook_entity_presave():

You can get the original entity object from $entity->original when it is an update of the entity.

So something like this ought to work:

function foo_node_presave(\Drupal\node\NodeInterface $node) {
  if (!$node->isNew() && $node->get('field_bar')->getValue() != $node->original->get('field_bar')->getValue()) {
    // ...
  • Thank you very much for your answer. I checked it and works as expected. I have a minor question though... I would expect the hook function's name to be foo_entity_presave and not foo_node_presave. Am I missing something here? While I cannot find the hook_node_presave in the drupal 8 API documentation, it seems that the function foo_node_presave is working. Do I miss something regarding the hook functions naming conventions? – Pantelis Natsiavas Jan 15 '17 at 14:39
  • 1
    Yeah it's just another naming convention, I probably should have linked you here as well: api.drupal.org/api/drupal/… – Clive Jan 15 '17 at 15:28

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