Increase the length of field without losing data in drupal 8

in this post, I'll show you how to increase the length of field without losing data in drupal 8.

Question

How to increase the length of field to 255 without losing data.

Solution

use hook_update_N() to chnage the length of field to 255 in database, configuration, and in storage schema. like the example below.

mymodule.install

<?php

use Drupal\field\Entity\FieldStorageConfig;

/**
 * @param $sandbox
 */
function mymodule_update_90005(&$sandbox) {
  $entity_type = 'node';
  $field_name = 'field_description';
  $field_length = 255;

  $database = \Drupal::database();
  // Resize the main field data table.
  $database->query("ALTER TABLE {$entity_type}__{$field_name} MODIFY {$field_name}_value VARCHAR({$field_length})");
  // Resize the revision field data table.
  $database->query("ALTER TABLE {$entity_type}_revision__{$field_name} MODIFY {$field_name}_value VARCHAR({$field_length})");

  // Update storage schema.
  $storage_key = $entity_type . '.field_schema_data.' . $field_name;
  $storage_schema = \Drupal::keyValue('entity.storage_schema.sql');
  $field_schema = $storage_schema->get($storage_key);
  $field_schema[$entity_type . '__' . $field_name]['fields'][$field_name . '_value']['length'] = $field_length;
  $field_schema[$entity_type . '_revision__' . $field_name]['fields'][$field_name . '_value']['length'] = $field_length;
  $storage_schema->set($storage_key, $field_schema);

  // Update field configuration.
  $config = \Drupal::configFactory()
    ->getEditable("field.storage.{$entity_type}.{$field_name}");
  $config->set('settings.max_length', $field_length);
  $config->save(TRUE);

  // Update field storage configuration.
  FieldStorageConfig::loadByName($entity_type, $field_name)->save();

  return t('Length of @entity-type.@field-name updated to @field-length', [
    '@entity-type' => $entity_type,
    '@field-name' => $field_name,
    '@field-length' => $field_length,
  ]);
}