Extending Drupal 8 Fields That Contain Data

function mycustom_update_8001() {
  // Variables to add the format column and its index
  $table  = 'field_page_header_content';
  $column = 'format';
  $field  = [
    'type'   => 'varchar_ascii',
    'length' => 255,
  ];
  $schema = Database::getConnection()->schema();
 
  // Update the data table
  $schema->addField('node__' . $table, $table . '_' . $column, $field);
  $schema->addIndex('node__' . $table, $table . '_' . $column, [$table . '_' . $column], [
    'fields' => [$table . '_' . $column => $field]
  ]);
  // The revision table
  $schema->addField('node_revision__' . $table, $table . '_' . $column, $field);
  $schema->addIndex('node_revision__' . $table, $table . '_' . $column, [$table . '_' . $column], [
    'fields' => [$table . '_' . $column => $field]
  ]);
  ...
}

function mycustom_update_8001() {
  ...
  // Force the current configuration to be exactly like the YAML,
  // so that the subsequent import does not detect a change
  $config              = \Drupal::configFactory()
    ->getEditable('field.storage.node.field_page_header_content');
  $depends             = $config->get('dependencies');
  $depends['module'][] = 'text';
  $config->set('dependencies', $depends);
  $config->set('type', 'text_long');
  $config->set('settings', []);
  $config->set('module', 'text');
  $config->save();
  ...
}

function mycustom_update_8001() {
  ...
  // Current node field configurations
  $field_manager = \Drupal::getContainer()->get('entity_field.manager');
  // Because the manager was already loaded before the above config was forced,
  // it will return the old configuration that was cached and so the cache needs clearing
  $field_manager->clearCachedFieldDefinitions();
  $field_storage_configs = $field_manager->getFieldStorageDefinitions('node');
 
  // Get the last installed configuration manager
  // This is the gatekeeper that determines if an update is needed or can be done
  $last_installed_repo = \Drupal::getContainer()->get('entity.last_installed_schema.repository');
 
  // Get the last installed configurations for all node fields
  // These are iterative objects and need to stored as such, not just native arrays,
  // so reusing the previously set configuration tree is not an option
  $last_installed_configs = $last_installed_repo->getLastInstalledFieldStorageDefinitions('node');
 
  // Force the last installed config to be the current for the field
  $last_installed_configs['field_page_header_content'] = $field_storage_configs['field_page_header_content'];
  $last_installed_repo->setLastInstalledFieldStorageDefinitions('node', $last_installed_configs);
}

function mycustom_update_8001() {
  // Set up date to add the format column
  $table  = 'field_page_header_content';
  $column = 'format';
  $field  = [
    'type'   => 'varchar_ascii',
    'length' => 255,
  ];
  $schema = Database::getConnection()->schema();
 
  // Update the data table
  $schema->addField('node__' . $table, $table . '_' . $column, $field);
  $schema->addIndex('node__' . $table, $table . '_' . $column, [$table . '_' . $column], [
    'fields' => [$table . '_' . $column => $field]
  ]);
  // The revision table
  $schema->addField('node_revision__' . $table, $table . '_' . $column, $field);
  $schema->addIndex('node_revision__' . $table, $table . '_' . $column, [$table . '_' . $column], [
    'fields' => [$table . '_' . $column => $field]
  ]);
 
  // Force the current configuration to be exactly like the YAML,
  // so that the subsequent import does not detect a change
  $config              = \Drupal::configFactory()
    ->getEditable('field.storage.node.field_page_header_content');
  $depends             = $config->get('dependencies');
  $depends['module'][] = 'text';
  $config->set('dependencies', $depends);
  $config->set('type', 'text_long');
  $config->set('settings', []);
  $config->set('module', 'text');
  $config->save();
 
  // Current node field configurations
  $field_manager = \Drupal::getContainer()->get('entity_field.manager');
  // Because the manager was already loaded before the above config was forced,
  // it will return the old configuration that was cached
  $field_manager->clearCachedFieldDefinitions();
  $field_storage_configs = $field_manager->getFieldStorageDefinitions('node');
 
  // Get the last installed manager, this is the gatekeeper that determines if
  // an update is needed or can be done
  $last_installed_repo = \Drupal::getContainer()->get('entity.last_installed_schema.repository');
 
  // Get the last installed configurations for node fields
  // These are iterative objects and need to stored as such, not just simple arrays,
  // so reusing the previously set configs is not an option
  $last_installed_configs = $last_installed_repo->getLastInstalledFieldStorageDefinitions('node');
 
  // Force the last installed config to be the current for the field
  $last_installed_configs['field_page_header_content'] = $field_storage_configs['field_page_header_content'];
  $last_installed_repo->setLastInstalledFieldStorageDefinitions('node', $last_installed_configs);
}