Return to Revisions

Drupal 7

When creating a text field in Drupal 7, you must a choose a maximum length for your data. As soon as you create any data for this field, the maximum length become immutable in the Drupal field settings.

It's understandable that this would be disabled for decreasing the maximum length because it could results in a loss of data, however, it should be possible to increase the maximum length for any field. A todo in the Drupal 7 Text module code shows this was intended but never accomplished.

The 3 things that need to happen:

1. Change the VARCHAR length of the value column in the field_data_{fieldname} table
2. Change the VARCHAR length of the value column in the field_revision_{fieldname} table
3. Update the configuration of the field to reflect the new max length setting The following function accomplishes all 3 of these steps and takes 2 easy parameters including the name of the field and the new maximum length.

/**
 * Helper function to change the max length of a text field.
 */
function MYMODULE_change_text_field_max_length($field_name, $new_length) {
  $field_table = 'field_data_' . $field_name;
  $field_revision_table = 'field_revision_' . $field_name;
  $field_column = $field_name . '_value';
 
  // Alter value field length in fields table.
  db_query("UPDATE `{$field_table}` SET `{$field_column}`=SUBSTR(`{$field_column}`, 0, {$new_length})");
  db_query("ALTER TABLE `{$field_table}` CHANGE `{$field_column}` `{$field_column}` VARCHAR( {$new_length} )");
  // Alter value field length in fields revision table.
  db_query("UPDATE `{$field_revision_table}` SET `{$field_column}`=SUBSTR(`{$field_column}`, 0, {$new_length})");
  db_query("ALTER TABLE `{$field_revision_table}` CHANGE `{$field_column}` `{$field_column}` VARCHAR( {$new_length} )");
 
  // Update field config with new max length.
  $result = db_query("SELECT CAST(`data` AS CHAR(10000) CHARACTER SET utf8) FROM `field_config` WHERE field_name = '{$field_name}'");
  $config = $result->fetchField();
  $config_array = unserialize($config);
  $config_array['settings']['max_length'] = $new_length;
  $config = serialize($config_array);
  db_update('field_config')
    ->fields(array('data' => $config))
    ->condition('field_name', $field_name)
    ->execute();
}

Once this function is available in your custom install file you can create a new database update function that uses this new function to make your required changes.

/**
 * Change max_length of Name field
 */
function mymodule_update_7002() {
  MYMODULE_change_text_field_max_length('field_name', 50);
}

^{Source: http://nathan.rambeck.org/blog/42-modify-drupal-7-text-field-maximum-length}

Drupal 8

Here is the version of the same function proposed by @Christopher:

/**
 * Utility to change the max length of a text field.
 *
 * @param string $field_name
 *   Field name. 
 * @param int $new_length
 *   Field length in characters. 
 *
 * @throws \DrupalUpdateException
 */
function MYMODULE_change_text_field_max_length($field_name, $new_length) {
  // The transaction opens here. 
  $txn = db_transaction();

  try {
    // Update field content tables with new max length.
    foreach (['field_data_', 'field_revision_'] as $prefix) {
      db_query('
      ALTER TABLE {' . $prefix . $field_name . '} 
        MODIFY ' . $field_name . '_value VARCHAR( ' . $new_length . ' )
      ');
    }

    // Update field config record with new max length.
    $result = db_query("
        SELECT CAST(data AS CHAR(10000) CHARACTER SET utf8) 
        FROM {field_config} 
        WHERE field_name = :field_name
      ", [':field_name' => $field_name]
    );
    $config = $result->fetchField();
    if ($config) {
      $config_array = unserialize($config);
      $config_array['settings']['max_length'] = $new_length;
      $new_config = serialize($config_array);
      db_update('field_config')
        ->fields(['data' => $new_config])
        ->condition('field_name', $field_name)
        ->execute();
    }
  }
  catch (Exception $e) {
    // Something went wrong somewhere, so roll back now.
    $txn->rollback();
    // Allow update to be re-run when errors are fixed.
    throw new \DrupalUpdateException(
      "Failed to change $field_name field max length: " . $e->getMessage(),
      $e->getCode(), $e
    );
  }
}