drupal/core/modules/comment/comment.install

<?php

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

use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\field\Entity\FieldStorageConfig;

/**
 * Implements hook_uninstall().
 */
function comment_uninstall() {
  // Remove the comment fields.
  $fields = entity_load_multiple_by_properties('field_storage_config', array('type' => 'comment'));
  foreach ($fields as $field) {
    $field->delete();
  }

  // Remove state setting.
  \Drupal::state()->delete('comment.node_comment_statistics_scale');
}

/**
 * Implements hook_install().
 */
function comment_install() {
  // By default, maintain entity statistics for comments.
  // @see \Drupal\comment\CommentStatisticsInterface
  \Drupal::state()->set('comment.maintain_entity_statistics', TRUE);
}

/**
 * Implements hook_schema().
 */
function comment_schema() {
  $schema['comment_entity_statistics'] = array(
    'description' => 'Maintains statistics of entity and comments posts to show "new" and "updated" flags.',
    'fields' => array(
      'entity_id' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => 'The entity_id of the entity for which the statistics are compiled.',
      ),
      'entity_type' => array(
        'type' => 'varchar_ascii',
        'not null' => TRUE,
        'default' => 'node',
        'length' => EntityTypeInterface::ID_MAX_LENGTH,
        'description' => 'The entity_type of the entity to which this comment is a reply.',
      ),
      'field_name' => array(
        'type' => 'varchar_ascii',
        'not null' => TRUE,
        'default' => '',
        'length' => FieldStorageConfig::NAME_MAX_LENGTH,
        'description' => 'The field_name of the field that was used to add this comment.',
      ),
      'cid' => array(
        'type' => 'int',
        'not null' => TRUE,
        'default' => 0,
        'description' => 'The {comment}.cid of the last comment.',
      ),
      'last_comment_timestamp' => array(
        'type' => 'int',
        'not null' => TRUE,
        'default' => 0,
        'description' => 'The Unix timestamp of the last comment that was posted within this node, from {comment}.changed.',
      ),
      'last_comment_name' => array(
        'type' => 'varchar',
        'length' => 60,
        'not null' => FALSE,
        'description' => 'The name of the latest author to post a comment on this node, from {comment}.name.',
      ),
      'last_comment_uid' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => 'The user ID of the latest author to post a comment on this node, from {comment}.uid.',
      ),
      'comment_count' => array(
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
        'default' => 0,
        'description' => 'The total number of comments on this entity.',
      ),
    ),
    'primary key' => array('entity_id', 'entity_type', 'field_name'),
    'indexes' => array(
      'last_comment_timestamp' => array('last_comment_timestamp'),
      'comment_count' => array('comment_count'),
      'last_comment_uid' => array('last_comment_uid'),
    ),
    'foreign keys' => array(
      'last_comment_author' => array(
        'table' => 'users',
        'columns' => array(
          'last_comment_uid' => 'uid',
        ),
      ),
    ),
  );

  return $schema;
}