Entity reference multi-select

Question

I'm trying to make an entity reference field a multi-select options select but I can't seem to find out how to make that happen. Any help is appreciated. Below is the code I'm using.

$fields['some_field'] = BaseFieldDefinition::create('entity_reference')
  ->setLabel(t('Some Field'))
  ->setDescription(t('This is a field.'))
  ->setRevisionable(TRUE)
  ->setSetting('target_type', 'other_entity')
  ->setSetting('handler', 'default')
  ->setTranslatable(TRUE)
  ->setDisplayOptions('view', [
    'label' => 'hidden',
    'type' => 'author',
    'weight' => 0,
  ])
  ->setDisplayOptions('form', [
    'type' => 'options_select',
    'weight' => 0,
    'settings' => [
      'options_select' => 'multiple',
      'placeholder' => '',
    ],
  ])
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE)
  ->setRequired(FALSE);

Answer 1

Ultimately this was answered in a different but similar question I asked. The answer is the code below attached to the field in my entity.

use Drupal\Core\Field\FieldStorageDefinitionInterface;

->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED) 

Answer 2

You can by using BaseFieldDefinition::setCardinality

Sets the maximum number of items allowed for the field.

By adding:

->setCardinality(0) 
// 0 means unlimited. Put 3 if you only want to allow up to 3 values