Change the Text Field Maximum Length in Drupal 8

Once a text field has data stored, it is not very easy or obvious how to change its maximum length. In the UI there is a message warning you that the field cannot be changed, because there is existing data. Sometimes it is necessary to change these values. It seems that there are a few ways and some resources to do this in Drupal 7, but I could not find a way to do this in Drupal 8. I decided to create a small function to do it:

Caution: Any change in the database needs to be done carefully. Before you continue please create a backup of your database.

/**
 * Update the length of a text field which already contains data.
 *
 * @param string $entity_type_id
 * @param string $field_name
 * @param integer $new_length
 */
function _module_change_text_field_max_length ($entity_type_id, $field_name, $new_length) {
  $name = 'field.storage.' . $entity_type_id . "." . $field_name;

  // Get the current settings
  $result = \Drupal::database()->query(
    'SELECT data FROM {config} WHERE name = :name',
    [':name' => $name]
  )->fetchField();
  $data = unserialize($result);
  $data['settings']['max_length'] = $new_length;

  // Write settings back to the database.
  \Drupal::database()->update('config')
    ->fields(['data' => serialize($data)])
    ->condition('name', $name)
    ->execute();

  // Update the value column in both the _data and _revision tables for the field
  $table = $entity_type_id . "__" . $field_name;
  $table_revision = $entity_type_id . "_revision__" . $field_name;
  $new_field = ['type' => 'varchar', 'length' => $new_length];
  $col_name = $field_name . '_value';
  \Drupal::database()->schema()->changeField($table, $col_name, $col_name, $new_field);
  \Drupal::database()->schema()->changeField($table_revision, $col_name, $col_name, $new_field);

  // Flush the caches.
  drupal_flush_all_caches();
}

This method needs the name of the entity, the name of the field, and the name and the new length.

And we can use it like this:

   _module_change_text_field_max_length('node', 'field_text', 280);

Usually, this code should be placed in (or called from) a hook_update so it will be executed automatically in the update.

And if the new length is too long to be placed in a regular input area, you can use the Textarea widget for text fields which will allow you to use the larger text area form element for text fields.