TestObjectItem.php

<?php

namespace Drupal\field_test\Plugin\Field\FieldType;

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

/**
 * Defines the 'test_object_field' entity field item.
 *
 * @FieldType(
 *   id = "test_object_field",
 *   label = @Translation("Test object field"),
 *   description = @Translation("Test field type that has an object to test serialization"),
 *   default_widget = "test_object_field_widget",
 *   default_formatter = "object_field_test_default"
 * )
 */
class TestObjectItem extends FieldItemBase {
    
    /**
     * {@inheritdoc}
     */
    public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
        $properties['value'] = DataDefinition::create('any')->setLabel(t('Value'))
            ->setRequired(TRUE);
        return $properties;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function schema(FieldStorageDefinitionInterface $field_definition) {
        return [
            'columns' => [
                'value' => [
                    'description' => 'The object item value.',
                    'type' => 'blob',
                    'not null' => TRUE,
                    'serialize' => TRUE,
                ],
            ],
        ];
    }

}