+ // Get a list of pre-existing references.
+ $previously_referenced_ids = [];
+ if ($value->getParent() && ($entity = $value->getEntity()) && !$entity->isNew()) {
+ $existing_entity = $this->entityTypeManager->getStorage($entity->getEntityTypeId())->loadUnchanged($entity->id());
+ foreach ($existing_entity->{$value->getFieldDefinition()->getName()}->getValue() as $item) {
+ $previously_referenced_ids[$item['target_id']] = $item['target_id'];
+ }
+ }
+