/**
 * Implements hook_field_storage_write().
 */
function {{ machine_name }}_field_storage_write($entity_type, $entity, $op, $fields) {
  list($id, $vid, $bundle) = entity_extract_ids($entity_type, $entity);
  if (!isset($vid)) {
    $vid = $id;
  }

  foreach ($fields as $field_id) {
    $field = field_info_field_by_id($field_id);
    $field_name = $field['field_name'];
    $table_name = _field_sql_storage_tablename($field);
    $revision_name = _field_sql_storage_revision_tablename($field);

    $all_languages = field_available_languages($entity_type, $field);
    $field_languages = array_intersect($all_languages, array_keys((array) $entity->$field_name));

    // Delete and insert, rather than update, in case a value was added.
    if ($op == FIELD_STORAGE_UPDATE) {
      // Delete languages present in the incoming $entity->$field_name.
      // Delete all languages if $entity->$field_name is empty.
      $languages = !empty($entity->$field_name) ? $field_languages : $all_languages;
      if ($languages) {
        db_delete($table_name)
          ->condition('entity_type', $entity_type)
          ->condition('entity_id', $id)
          ->condition('language', $languages, 'IN')
          ->execute();
        db_delete($revision_name)
          ->condition('entity_type', $entity_type)
          ->condition('entity_id', $id)
          ->condition('revision_id', $vid)
          ->condition('language', $languages, 'IN')
          ->execute();
      }
    }

    // Prepare the multi-insert query.
    $do_insert = FALSE;
    $columns = array('entity_type', 'entity_id', 'revision_id', 'bundle', 'delta', 'language');
    foreach ($field['columns'] as $column => $attributes) {
      $columns[] = _field_sql_storage_columnname($field_name, $column);
    }
    $query = db_insert($table_name)->fields($columns);
    $revision_query = db_insert($revision_name)->fields($columns);

    foreach ($field_languages as $langcode) {
      $items = (array) $entity->{$field_name}[$langcode];
      $delta_count = 0;
      foreach ($items as $delta => $item) {
        // We now know we have something to insert.
        $do_insert = TRUE;
        $record = array(
          'entity_type' => $entity_type,
          'entity_id' => $id,
          'revision_id' => $vid,
          'bundle' => $bundle,
          'delta' => $delta,
          'language' => $langcode,
        );
        foreach ($field['columns'] as $column => $attributes) {
          $record[_field_sql_storage_columnname($field_name, $column)] = isset($item[$column]) ? $item[$column] : NULL;
        }
        $query->values($record);
        if (isset($vid)) {
          $revision_query->values($record);
        }

        if ($field['cardinality'] != FIELD_CARDINALITY_UNLIMITED && ++$delta_count == $field['cardinality']) {
          break;
        }
      }
    }

    // Execute the query if we have values to insert.
    if ($do_insert) {
      $query->execute();
      $revision_query->execute();
    }
  }
}