class EntityTest

class EntityTest extends ContentEntityBase implements EntityOwnerInterface {

  /**
   * {@inheritdoc}
   */
  public static function preCreate(EntityStorageInterface $storage, array &$values) {
    parent::preCreate($storage, $values);
    if (empty($values['type'])) {
      $values['type'] = $storage
        ->getEntityTypeId();
    }
  }

  /**
   * {@inheritdoc}
   */
  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
    $fields = parent::baseFieldDefinitions($entity_type);
    $fields['name'] = BaseFieldDefinition::create('string')
      ->setLabel(t('Name'))
      ->setDescription(t('The name of the test entity.'))
      ->setTranslatable(TRUE)
      ->setSetting('max_length', 64)
      ->setDisplayOptions('view', [
      'label' => 'hidden',
      'type' => 'string',
      'weight' => -5,
    ])
      ->setDisplayOptions('form', [
      'type' => 'string_textfield',
      'weight' => -5,
    ]);
    $fields['created'] = BaseFieldDefinition::create('created')
      ->setLabel(t('Authored on'))
      ->setDescription(t('Time the entity was created'))
      ->setTranslatable(TRUE);
    $fields['user_id'] = BaseFieldDefinition::create('entity_reference')
      ->setLabel(t('User ID'))
      ->setDescription(t('The ID of the associated user.'))
      ->setSetting('target_type', 'user')
      ->setSetting('handler', 'default')
      ->setDefaultValue([
      0 => [
        'target_id' => 1,
      ],
    ])
      ->setTranslatable(TRUE)
      ->setDisplayOptions('form', [
      'type' => 'entity_reference_autocomplete',
      'weight' => -1,
      'settings' => [
        'match_operator' => 'CONTAINS',
        'size' => '60',
        'placeholder' => '',
      ],
    ]);
    return $fields + \Drupal::state()
      ->get($entity_type
      ->id() . '.additional_base_field_definitions', []);
  }

  /**
   * {@inheritdoc}
   */
  public function getOwner() {
    return $this
      ->get('user_id')->entity;
  }

  /**
   * {@inheritdoc}
   */
  public function getOwnerId() {
    return $this
      ->get('user_id')->target_id;
  }

  /**
   * {@inheritdoc}
   */
  public function setOwnerId($uid) {
    $this
      ->set('user_id', $uid);
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function setOwner(UserInterface $account) {
    $this
      ->set('user_id', $account
      ->id());
    return $this;
  }

  /**
   * Sets the name.
   *
   * @param string $name
   *   Name of the entity.
   *
   * @return $this
   */
  public function setName($name) {
    $this
      ->set('name', $name);
    return $this;
  }

  /**
   * Returns the name.
   *
   * @return string
   */
  public function getName() {
    return $this
      ->get('name')->value;
  }

  /**
   * {@inheritdoc}
   */
  public function getEntityKey($key) {

    // Typically this protected method is used internally by entity classes and
    // exposed publicly through more specific getter methods. So that test cases
    // are able to set and access entity keys dynamically, update the visibility
    // of this method to public.
    return parent::getEntityKey($key);
  }

}