In code, only create a revision if a field is changed

Question

I have a custom revisionable entity with a few dozen fields. I'm importing data about the entity on a periodic basis. If the entity has changed, I'd like to save it and create a new revision.

$dogs = \Drupal::entityTypeManager()
  ->getStorage('my_entity')
  ->loadByProperties(['my_entity_id' => $my_entity_id]);

$dog = reset($dogs);

$dog->set('name', $record['TheName']);
$dog->set('birth_date', $record['Dog Birth Date']);
// Lots more ->set happening here.
$dog->set('notes', $record['Notes']);
if ($dog->someMagicComparisonFunction()) {
  $dog->setNewRevision(TRUE);
  $dog->save();
}

I searched for the someMagicComparisonFunction but didn't find it. Does it exist?

Answer 1

This may do the trick in a hook_entity_presave(), or get you close:

$old_dog = clone $dog;
update_the_dog($dog);

// Use == to allow for out of order keys.
$same = $dog->toArray() == $old_dog->toArray();

This is kinda of cheating, and you may want to filter the arrays for just the fields and not the properties. It also isn't multilingual-safe.

To do it properly, start reading ContentEntityBase::hasTranslationChanges() and FieldItemList::equals(). The code above makes a lot of assumptions about fields and storage, which ContentEntityBase() does properly.