How to replace allowed_values for a select field by external definition?

Question

I created a custom content entity, called member, with some fields of which one, called status, is a list appearing in form as a select:

$fields['status'] = BaseFieldDefinition::create('list_integer')
  ->setLabel(t('Statut'))
  ->setRequired(TRUE)
  ->setSettings(array(
    'allowed_values' => array(
      0 => 'Ancien',
      1 => 'Actif',
      2 => 'Non renouvelée',
      3 => 'Renouvelée',
      4 => 'En attente',
    ),
  ))
  ->setDefaultValue(4)
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'weight' => 7,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'options_select',
    'weight' => 7,
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

I'd like to put the definition of the allowed values 'somewhere else' (meaning not directly in the definition of the member entity).
I know I could create another content entity (e.g. possible_status) that I would reference this way:

$fields['status'] = BaseFieldDefinition::create('entity_reference')
  ->setSetting('target_type', 'possible_status)')

But it seems a bit 'rich' to handle a couple of values...
Is there another way to store the values 'outside' the code defining the member entity?
An include file, a text file, a JSON file I could import?
What would be the best practice for that?

[EDIT]
I changed for this:

$fields['status'] = BaseFieldDefinition::create('list_integer')
  ->setLabel(t('Statut'))
  ->setRequired(TRUE)
  ->setSettings(['allowed_values_function' => 'association_allowed_values_function'])
  ->setDefaultValue(4)

with this in my module:

function association_allowed_values_function(FieldStorageDefinitionInterface $definition, FieldableEntityInterface $entity = NULL, &$cacheable = TRUE) {

  if ($definition['entity_type'] == 'member' && $definition'field_name' == 'status') {
    $values = [
      0 => 'Ancien',
      1 => 'Actif',
      2 => 'Non renouvelée',
      3 => 'Renouvelée',
      4 => 'En attente',
    ];
  }
  return $values;
}

and it works!

Now, I'd like to move association_allowed_values_function to an include file. And I don't know how...

Answer 1

Instead of allowed_values you can add a callback to set the allowed values:

  ->setSettings(['allowed_values_function' => 'callback_allowed_values_function'])

The callback:

function callback_allowed_values_function(FieldStorageDefinitionInterface $definition, FieldableEntityInterface $entity = NULL, &$cacheable = TRUE) {
  if (isset($entity) && ($entity->bundle() == 'not_a_programmer')) {
    $values = [
      1 => 'One',
      2 => 'Two',
    ];
  }
  else {
    $values = [
      'Group 1' => [
        0 => 'Zero',
        1 => 'One',
      ],
      'Group 2' => [
        2 => 'Two',
      ],
    ];
  }

  return $values;
}

You can get the allowed values from a text file or put the callback in an include file.

For more information see options.api.php

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A different approach might be to store the allowed values in config, for which there is a bundle specific base field override, see How to easily alter an entity's base field definition per bundle. Then you can manage the allowed values list in a yaml file of an exported config.