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.'))
  ->setSetting('target_type', 'other_entity')
  ->setSetting('handler', 'default')
  ->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)
up vote 1 down vote accepted

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;


You can by using BaseFieldDefinition::setCardinality

Sets the maximum number of items allowed for the field.

By adding:

// 0 means unlimited. Put 3 if you only want to allow up to 3 values

  • Thank you for the response. I added it to the entity but the form it still displays it as a drop down and not a multiple select list. I assume there is an setDisplayOptions option I need to apply to make this happen? After looking through the core code I couldn't seem to narrow that down. – themantimeforgot Dec 4 at 15:18
  • ->setCardinality(0) Didn't work for me or at least it didn't produce the outcome I was looking for. I asked a similar question but rather on the form display side of things and someone responded with the following similar answer that worked. ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED) – themantimeforgot Dec 6 at 16:09
  • @themantimeforgot in the link I provided, I actually missed reading Possible values are positive integers or FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED.. In D7 zero was used for unlimited, but clearly no longer the case for D8. – No Sssweat Dec 7 at 2:06

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