SqlContentEntityStorageSchema::createEntitySchemaIndexes

protected SqlContentEntityStorageSchema::createEntitySchemaIndexes(array $entity_schema, FieldStorageDefinitionInterface $storage_definition = NULL)

protected function createEntitySchemaIndexes(array $entity_schema, FieldStorageDefinitionInterface $storage_definition = NULL) {
  $schema_handler = $this->database->schema();

  if ($storage_definition) {
    $table_mapping = $this->storage->getTableMapping();
    $column_names = $table_mapping->getColumnNames($storage_definition->getName());
  }

  $index_keys = [
    'indexes' => 'addIndex',
    'unique keys' => 'addUniqueKey',
  ];

  foreach ($this->getEntitySchemaData($this->entityType, $entity_schema) as $table_name => $schema) {
    // Add fields schema because database driver may depend on this data to
    // perform index normalization.
    $schema['fields'] = $entity_schema[$table_name]['fields'];

    foreach ($index_keys as $key => $add_method) {
      if (!empty($schema[$key])) {
        foreach ($schema[$key] as $name => $specifier) {
          // If a set of field columns were specified we process only indexes
          // involving them. Only indexes for which all columns exist are
          // actually created.
          $create = FALSE;
          $specifier_columns = array_map(function($item) {
            return is_string($item) ? $item : reset($item);
          }, $specifier);
          if (!isset($column_names) || array_intersect($specifier_columns, $column_names)) {
            $create = TRUE;
            foreach ($specifier_columns as $specifier_column_name) {
              // This may happen when adding more than one field in the same
              // update run. Eventually when all field columns have been
              // created the index will be created too.
              if (!$schema_handler->fieldExists($table_name, $specifier_column_name)) {
                $create = FALSE;
                break;
              }
            }
          }
          if ($create) {
            $this->{$add_method}($table_name, $name, $specifier, $schema);
          }
        }
      }
    }
  }
}