How to rereference taxonomy?

Question

My goal was to create a taxonomy reference field in Drupal 8.2.

Consider these to field definitions on an entity.

    // #1
    $fields[$field] = BaseFieldDefinition::create('entity_reference')
        ->setTargetEntityTypeId('taxonomy_term')

    // #2
    $fields[$field] = BaseFieldDefinition::create('entity_reference')
        ->setSetting('target_type', 'taxonomy_term')

Here is how #1 is documented:

  /**
   * Sets the ID of the type of the entity this field is attached to.
   *
   * @param string $entity_type_id
   *   The name of the target entity type to set.
   *
   * @return $this
   */
  public function setTargetEntityTypeId($entity_type_id) {

Looking at the description both should produce the same result - set target entity type.

The #1 creates me an input with autocomplete from page names and page types.

The #2 creates n input with autocomplete from taxonomy terms.

Why does this happen and what is #1 is meant to do?

Answer 1

As I answered at Limit Taxonomy Term references to special vocabulary if you want to create a custom entity_reference field on custom entity type try something like

$fields['book_cat'] = BaseFieldDefinition::create('entity_reference')
   ->setLabel(t('LABEL'))
   ->setDescription(t('DESCRIPTION'))
   ->setSetting('target_type','taxonomy_term' )
   ->setSetting('handler','default' )
   ->setSetting('handler_settings',['target_bundles'=>['VOCAB_MACHINE_NAME'=>'VOCAB_MACHINE_NAME']] )
   ->setTranslatable(TRUE)
   ->setDisplayOptions('form', array(
       'type' => 'options_select',
       'weight' => -1,
       'settings' => array(
           'size' => '60',
           'placeholder' => '',
       ),
   ))
   ->setDisplayConfigurable('form', TRUE)
   ->setDisplayConfigurable('view', TRUE);

AND about setTargetEntityTypeId :(Doc)

Sets the ID of the type of the entity this field is attached to.

and used when you want attach field(s) not for referencing.