Truncate.php

<?php

namespace Drupal\Core\Database\Query;

use Drupal\Core\Database\Database;
use Drupal\Core\Database\Connection;

/**
 * General class for an abstracted TRUNCATE operation.
 */
class Truncate extends Query {
    
    /**
     * The table to truncate.
     *
     * @var string
     */
    protected $table;
    
    /**
     * Constructs a Truncate query object.
     *
     * @param \Drupal\Core\Database\Connection $connection
     *   A Connection object.
     * @param string $table
     *   Name of the table to associate with this query.
     * @param array $options
     *   Array of database options.
     */
    public function __construct(Connection $connection, $table, array $options = []) {
        // @todo Remove $options['return'] in Drupal 11.
        // @see https://www.drupal.org/project/drupal/issues/3256524
        $options['return'] = Database::RETURN_AFFECTED;
        parent::__construct($connection, $options);
        $this->table = $table;
    }
    
    /**
     * Executes the TRUNCATE query.
     *
     * @return int|null
     *   Return value is dependent on whether the executed SQL statement is a
     *   TRUNCATE or a DELETE. TRUNCATE is DDL and no information on affected
     *   rows is available. DELETE is DML and will return the number of affected
     *   rows. In general, do not rely on the value returned by this method in
     *   calling code.
     *
     * @see https://learnsql.com/blog/difference-between-truncate-delete-and-drop-table-in-sql
     */
    public function execute() {
        $stmt = $this->connection
            ->prepareStatement((string) $this, $this->queryOptions, TRUE);
        try {
            $stmt->execute([], $this->queryOptions);
            return $stmt->rowCount();
        } catch (\Exception $e) {
            $this->connection
                ->exceptionHandler()
                ->handleExecutionException($e, $stmt, [], $this->queryOptions);
        }
        return NULL;
    }
    
    /**
     * Implements PHP magic __toString method to convert the query to a string.
     *
     * @return string
     *   The prepared statement.
     */
    public function __toString() {
        // Create a sanitized comment string to prepend to the query.
        $comments = $this->connection
            ->makeComment($this->comments);
        // In most cases, TRUNCATE is not a transaction safe statement as it is a
        // DDL statement which results in an implicit COMMIT. When we are in a
        // transaction, fallback to the slower, but transactional, DELETE.
        // PostgreSQL also locks the entire table for a TRUNCATE strongly reducing
        // the concurrency with other transactions.
        if ($this->connection
            ->inTransaction()) {
            return $comments . 'DELETE FROM {' . $this->connection
                ->escapeTable($this->table) . '}';
        }
        else {
            return $comments . 'TRUNCATE {' . $this->connection
                ->escapeTable($this->table) . '} ';
        }
    }

}