<?php

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

/**
 * Implements hook_field_schema().
 */
function entity_reference_field_schema($field) {
  $schema = array(
    'columns' => array(
      'target_id' => array(
        'description' => 'The ID of the target entity.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => TRUE,
      ),
      'revision_id' => array(
        'description' => 'The revision ID of the target entity.',
        'type' => 'int',
        'unsigned' => TRUE,
        'not null' => FALSE,
      ),
    ),
    'indexes' => array(
      'target_id' => array('target_id'),
    ),
  );

  // Create a foreign key to the target entity type base type.
  $entity_manager = Drupal::service('plugin.manager.entity');
  if (is_subclass_of($entity_manager->getControllerClass($field['settings']['target_type'], 'storage'), 'Drupal\Core\Entity\DatabaseStorageController')) {
    $entity_info = $entity_manager->getDefinition($field['settings']['target_type']);

    $base_table = $entity_info['base_table'];
    $id_column = $entity_info['entity_keys']['id'];

    $schema['foreign keys'][$base_table] = array(
      'table' => $base_table,
      'columns' => array('target_id' => $id_column),
    );
  }

  return $schema;
}