How can one programmatically get the bundle constraint for an entity reference field?

Question

I'm working in the context of a Views plugin. I have $entity_type and $field, as required in the snippet below. How can I get the bundle constraint for the entity reference field programmatically?

/** @var Drupal\field\Entity\FieldStorageConfig $field_configuration */
$field_configuration = FieldStorageConfig::loadByName($entity_type, $field);

$field_configuration->getType() gives me "entity_reference"

$field_configuration->getSettings()['target_type'] gives me "taxonomy_term"

...but what methods return the vocabulary or vocabularies (bundles) that the entity reference field is set to be limited by (if at all) in its configuration?

Answer 1

The types allowed by an entity reference field is stored in the field config (FieldConfig.php and the field.field.* yaml), not the field storage config (FieldStorageConfig.php and the field.storage.* yaml).

If you take a peek at one instance of a field.field.* yaml of an entity reference field, you'll see the settings.handler_settings.target_bundle property containing a list of allowed bundles for that entity reference field. To get this data from code, you'll need FieldConfig::load(id) or FieldConfig::loadByName($entity_type_id, $bundle, $field_name) depending on what data you have at hand. Once you get the field config instance, there is a getSetting() method which you can use to grab handler_settings.