Date.php

<?php

namespace Drupal\datetime\Plugin\views\sort;

use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
use Drupal\views\FieldAPIHandlerTrait;
use Drupal\views\Plugin\views\sort\Date as NumericDate;

/**
 * Basic sort handler for datetime fields.
 *
 * This handler enables granularity, which is the ability to make dates
 * equivalent based upon nearness.
 *
 * @ViewsSort("datetime")
 */
class Date extends NumericDate {
    use FieldAPIHandlerTrait;
    
    /**
     * Determines if the timezone offset is calculated.
     *
     * @var bool
     */
    protected $calculateOffset = TRUE;
    
    /**
     * {@inheritdoc}
     */
    public function __construct(array $configuration, $plugin_id, $plugin_definition) {
        parent::__construct($configuration, $plugin_id, $plugin_definition);
        $definition = $this->getFieldStorageDefinition();
        if ($definition->getSetting('datetime_type') === DateTimeItem::DATETIME_TYPE_DATE) {
            // Timezone offset calculation is not applicable to dates that are stored
            // as date-only.
            $this->calculateOffset = FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     *
     * Override to account for dates stored as strings.
     */
    public function getDateField() {
        // Use string date storage/formatting since datetime fields are stored as
        // strings rather than UNIX timestamps.
        return $this->query
            ->getDateField("{$this->tableAlias}.{$this->realField}", TRUE, $this->calculateOffset);
    }
    
    /**
     * {@inheritdoc}
     *
     * Overridden in order to pass in the string date flag.
     */
    public function getDateFormat($format) {
        return $this->query
            ->getDateFormat($this->getDateField(), $format, TRUE);
    }

}