farm-2.x-dev/modules/core/id_tag/src/Plugin/Field/FieldType/IdTagItem.php

<?php

namespace Drupal\farm_id_tag\Plugin\Field\FieldType;

use Drupal\Core\Field\FieldItemBase;
use Drupal\Core\Field\FieldStorageDefinitionInterface;
use Drupal\Core\TypedData\DataDefinition;

/**
 * Plugin implementation of the 'ID tag' field type.
 *
 * @FieldType(
 *   id = "id_tag",
 *   label = @Translation("ID tag"),
 *   description = @Translation("This field stores a combination of id, tag type and location."),
 *   no_ui = TRUE,
 *   default_widget = "id_tag",
 *   default_formatter = "id_tag"
 * )
 */
class IdTagItem extends FieldItemBase {

  /**
   * {@inheritdoc}
   */
  public static function schema(FieldStorageDefinitionInterface $field_definition) {
    return [
      'columns' => [
        'id' => [
          'description' => 'The id of the tag.',
          'type' => 'varchar',
          'length' => 8192,
          'not null' => TRUE,
        ],
        'type' => [
          'description' => 'The type of the tag.',
          'type' => 'varchar',
          'length' => 255,
          'not null' => TRUE,
        ],
        'location' => [
          'description' => 'The location of the tag.',
          'type' => 'varchar',
          'length' => 1024,
          'not null' => TRUE,
        ],
      ],
    ];
  }

  /**
   * {@inheritdoc}
   */
  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
    $properties['id'] = DataDefinition::create('string')
      ->setLabel(t('ID of the tag'));
    $properties['type'] = DataDefinition::create('string')
      ->setLabel(t('Type of the tag'));
    $properties['location'] = DataDefinition::create('string')
      ->setLabel(t('Location of the tag'));
    return $properties;
  }

  /**
   * {@inheritdoc}
   */
  public function isEmpty() {
    $id = $this->get('id');
    $type = $this->get('type');
    $location = $this->get('location');
    return ($id === NULL || $id->getValue() === '') && ($type === NULL || $type->getValue() === '') && ($location === NULL || $location->getValue() === '');
  }

}