how to get all the fields that have been modified on entity save (form submit)?

Question

I am trying to figure out an efficient way to get the fields names/values that have been updated. It's kind of similar to what the diff module does to calculate changed on a node but not as detailed. I just want to see what fields have been updated when a user saves an entity. For example a user may not change the title but could change the body. I would like to build an api function returns that. something like this pseudo code:

// possibly on presave or form submit. 
function my_module_entity_presave() {
    // Return only the fields values that are not similar to the original node: 
    $modified = $entity->getModifiedFields();
}

and the method could be something like this psudo code:

public function getModifiedFields() {
  $original = $this->originalFieldsValues();
  $new = $this->newFieldValues();
  // compare original with new
  // finally return only modified fields name values.
  $modified = ['title' => 'new value', 'body' => 'new value' ...];
  return $modified 
}

Answer 1

When you are in the presave hook, the updated $node object will have $node->original, which is the node before things were changed.

Nodes also have a $node->toArray(), method that will flatten the object into a multidimensional associative array.

So, this

array_keys(DiffArray::diffAssocRecursive($node->toArray(), $node->original->toArray())

should

1. Take the $node and $node->original and convert them into arrays.
2. Run the two arrays through one of the Drupal helper classes that will generate differences in multidimensional associative arrays.
3. Return the top level keys. Because of the ways nodes are built, this will be all of the changed property and field names.

Answer 2

Here's an excerpt from a method I use to determine if an entity has changed. I adapted it a little bit to return the names for you. You may need to adapt it more for your specific needs.

mymodule > src > GaryFunctions.php

<?php

/**
 * File for holding helper functions user by Gary
 */


namespace Drupal\mymodule;

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\FieldableEntityInterface;
use Drupal\Core\Entity\Entity\EntityViewDisplay;

class GaryFunctions {

  /**
   * Check if entity field content has changed
   * @param  EntityInterface $entity     The entity being saved
   * @return array                    A list of changed field names
   */
  public function entityHasChanged(EntityInterface $entity) {
    $changed_fields = [];
    if (!$entity->original) {
      return $changed_fields;
    }
    $field_names = $this->getFieldList($entity->bundle(), $entity->getEntityTypeId());
    foreach($field_names as $key => $field_name) {
      if($entity->hasField($field_name) && $field_name != 'field_comments' && !$entity->get($field_name)->equals($entity->original->get($field_name))){
        $changed_fields[] = $field_name;
        // $entity->get($field_name)->getValue();
      }
    }
     return $changed_fields;
  }


  /**
   * Get list of field names from bundle
   * @param  string $bundle Bundle name
   * @return array         Array of field names
   */
  public function getFieldList($bundle, $entity_type_id) {
    $fields_by_weight = [];
    $bundle_fields = \Drupal::entityTypeManager()
      ->getStorage('entity_view_display')
      ->load($entity_type_id . '.' . $bundle . '.' . 'default')
      ->getComponents();

    foreach ($bundle_fields as $name => $options) {
      $fields_by_weight[] = $name;
    }
    return $fields_by_weight;
  }

}

mymodule > mymodule.module

<?php

use Drupal\Core\Entity\EntityInterface;
use Drupal\mymodule\GaryFunctions;

function mymodule_entity_presave(EntityInterface $entity) {
  $helper = new GaryFunctions;

  switch ($entity->bundle()){

    case 'projects':
      $changed_fields = $helper->entityHasChanged($entity);
      if (!empty($changed_fields)) {
        print_r($changed_fields);
      } else {
        print 'didnt change';
      }
    break;

    default:
    break;
  }

}

Answer 3

You can use $node->original, it does give access to the original node values, so lets assume that the field you desire check is foo_field :

function myModule_node_presave($node) {
  if ($node->getType() == 'my_content_type') {
    if ($node->original->foo_field != $node->foo_field) {
      // Do what you want here.
    }
  }
}