Drupal migration example

convert quote from varchar to text

// Update the table.
  $storage_definition = BaseFieldDefinition::create('string_long')
    ->setLabel(t('Quote'))
    ->setDescription(t('The quote, always treated as non-markup plain text.'))
    ->setRequired(TRUE)
    ->setTranslatable(TRUE)
    ->setDefaultValue('')
    ->setDisplayOptions('view', array(
      'label' => 'hidden',
      'type' => 'rd_quote',
      'weight' => -5,
    ))
    ->setDisplayOptions('form', [
      'type' => 'string_textarea',
      'weight' => -5,
      'settings' => [
        'rows' => 8,
      ],
    ])
    ->setDisplayConfigurable('form', TRUE);

  $storage_definition->setName('quote')
    ->setTargetEntityTypeId('rd_quote')
    ->setProvider('rd_quote')
    ->setTargetBundle(NULL);

  \Drupal::entityDefinitionUpdateManager()->updateFieldStorageDefinition($storage_definition);