How to remove reference field value after delete its reference node

Question

Let say, I have 2 nodes.
In first node, I add a reference to an existing node, e.g. Test node [nid:2]; I delete the referenced node. When I edit the first node,the reference field shows [nid:2].

How can I make that reference field empty, once the referenced node is deleted?

Answer 1

Try using Reference Delete module..

Project page says

Deletes values in reference fields created with Entity Reference or References when the referenced entity is deleted.

Answer 2

If you want to add code for that purpose to a custom module you already have, then you can use the code the Reference Delete module is using as guide.

In short, the code used in the 7.x-1 branch:

• When an entity is deleted, it adds its ID and type to a queue
• During cron task, delete the reference to the deleted entities found on the tables used from the reference fields

The first part is done implementing hook_entity_delete(). For the second part, this is the relevant code used from that module.

/**
 * Returns an array of fields, filtered by module.
 */
function _reference_delete_get_reference_fields($module) {
  $fields = field_info_field_map();

  $reference_fields = array();

  foreach ( $fields as $field_name => &$properties ) {
    $properties = field_info_field($field_name);

    if ($properties['module'] == $module) {
      $reference_fields[$field_name] = $properties;
    }
  }

  if ( !empty($reference_fields) ) {
    return $reference_fields;
  }
}

/**
 * Implements hook_reference_delete_delete_references().
 */
function entityreference_reference_delete_delete_references($entity_id, $type) {
  $module = 'entityreference';

  if ( $fields = _reference_delete_get_reference_fields($module) ) {
    foreach ( $fields as $field_name => $properties ) {
      // Acts only if the target entity is of the same type of the entity that's being deleted
      if ( $properties['settings']['target_type'] == $type ) {
        $tables = reset($properties['storage']['details']);

        foreach ( $tables as $table ) {
          $keys = array_keys($table);
          $table_name = reset($keys);
          $column_name = $table[$table_name]['target_id'];

          db_delete($table_name)
          ->condition($column_name, $entity_id, '=')
          ->execute();

          watchdog('reference_delete', 'Deleted all references to entity %entity_type #!entity_id from table !table', array('%entity_type' => $type, '!entity_id' => $entity_id, '!table' => $table_name), WATCHDOG_NOTICE);
        }
      }
    }
  }
}

/**
 * Implements hook_reference_delete_delete_references().
 */
function references_reference_delete_delete_references($entity_id, $type) {
  switch ($type) {
    case 'node' :
      $module = 'node_reference';

      if ( $fields = _references_reference_delete_make_table_names($module) ) {
        foreach ( $fields as $field => $tables ) {
          foreach ( $tables as $table ) {
            db_delete($table)
              ->condition($field . '_nid', $entity_id, '=')
              ->execute();

            watchdog('reference_delete', 'Deleted all references to entity %entity_type #!entity_id from table !table', array('%entity_type' => $type, '!entity_id' => $entity_id, '!table' => $table_name), WATCHDOG_NOTICE);
          }
        }
      }
    break;

    case 'user' :
      $module = 'user_reference';

      if ( $fields = _references_reference_delete_make_table_names($module) ) {
        foreach ( $fields as $field => $tables ) {
          foreach ( $tables as $table_name ) {
            db_delete($table_name)
              ->condition($field . '_uid', $entity_id, '=')
              ->execute();

            watchdog('reference_delete', 'Deleted all references to entity %entity_type #!entity_id from table !table', array('%entity_type' => $type, '!entity_id' => $entity_id, '!table' => $table_name), WATCHDOG_NOTICE);
          }
        }
      }
    break;
  }
}

/**
 * Creates table names (used only for References).
 */
function _references_reference_delete_make_table_names($module) {
  if (isset($module)) {
    $fields = _reference_delete_get_reference_fields($module);

    if ( count($fields) ) {
      $tables = array();
      foreach ( $fields as $field ) {

        $tables[$field] = array('field_data_' . $field, 'field_revision_' . $field);
      }

      return $tables;
    }
  }
}

hook_reference_delete_delete_references() is a hook used from that module. You don't need to implement it, but use that code to write a function, or a hook, for example hook_cron() or the worker callback of a queue, in the case you want to follow the same approach used from that module.

I would rather implement hook_entity_delete() and delete any reference to the deleted node from the tables used from the reference module being used.