How to uninstall a module that has added a basefield that has data

Question

My module adds a basefield 'myfield' to the core 'file' content entity.

I now need to uninstall my module for development purposes, but I can't because drush refuses to uninstall the module, saying "There is data for the field myfield on entity type File".

My understanding is that this is a known issue:

• Because my module adds this field to an entity it does not own, this uninstallation will not be taken care of automatically by the core uninnstall procedure,

• Therefore my module needs to have a hook_uninstall that triggers field uninstallation using \Drupal::entityDefinitionUpdateManager()->uninstallFieldStorageDefinition

• However, a field can't be uninstalled if it still has data in it, so I first need to remove the data.

• But the system to purge field data currently only works for bundle fields not base fields.

• There may be other ways to delete field data, but they won't scale to large quantities of data.

• Therefore there is no robust way to uninstall my module and Drupal core is correct to refuse to uninstall it.

Given all that, how best can I uninstall it when I need to do so for development purposes (short of reinstalling Drupal)?

Here is how I am creating it:

In mymodule.module:

function mymodule_entity_base_field_info(\Drupal\Core\Entity\EntityTypeInterface $entity_type) {
  if ($entity_type->id() == 'file') {
    $fields = array();
    $fields['myfield'] = BaseFieldDefinition::create('boolean')
      ->setLabel(t('My field'))
    return $fields;
  }
}

In mymodule.install:

  $entity_manager = \Drupal::entityManager();
  $definition = $entity_manager->getFieldStorageDefinitions('file')['myfield'];
  $entity_manager->onFieldStorageDefinitionCreate($definition);

Answer 1

This is a known Drupal Core limitation that looks close to being ready so hopefully will be fixed in D8.5. In the meantime you could apply the patch linked to the issue.

Answer 2

Does drush field-delete myfieldname work for base fields? If so, you could look in drush's source code to see how it accomplishes this.

I don't see any information regarding this in the drush 8.x documentation.