drupal/core/modules/book/book.install

<?php

/**
 * @file
 * Install, update and uninstall functions for the book module.
 */

/**
 * Implements hook_uninstall().
 */
function book_uninstall() {
  // Delete menu links.
  db_delete('menu_links')
    ->condition('module', 'book')
    ->execute();
  menu_cache_clear_all();
}

/**
 * Implements hook_schema().
 */
function book_schema() {
  $schema['book'] = array(
  'description' => 'Stores book outline information. Uniquely connects each node in the outline to a link in {menu_links}',
    'fields' => array(
      'mlid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => "The book page's {menu_links}.mlid.",
      ),
      'nid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => "The book page's {node}.nid.",
      ),
      'bid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => "The book ID is the {book}.nid of the top-level page.",
      ),
    ),
    'primary key' => array('mlid'),
    'unique keys' => array(
      'nid' => array('nid'),
    ),
    'indexes' => array(
      'bid' => array('bid'),
    ),
  );

  return $schema;
}

/**
 * Move the Book module settings from variables to config.
 *
 * @ingroup config_upgrade
 */
function book_update_8000() {
  update_variables_to_config('book.settings', array(
    'book_child_type' => 'child_type',
    'book_block_mode' => 'block.navigation.mode',
  ));
  $allowed_types = update_variable_get('book_allowed_types', FALSE);
  if ($allowed_types) {
    // Ensure consistent ordering of allowed_types.
    // @see book_admin_settings_submit()
    sort($allowed_types);

    \Drupal::config('book.settings')
      ->set('allowed_types', $allowed_types)
      ->save();
  }

}