class DatabaseStorage

class DatabaseStorage extends StorageBase {
    use DependencySerializationTrait;
    
    /**
     * The serialization class to use.
     *
     * @var \Drupal\Component\Serialization\SerializationInterface
     */
    protected $serializer;
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * The name of the SQL table to use.
     *
     * @var string
     */
    protected $table;
    
    /**
     * Overrides Drupal\Core\KeyValueStore\StorageBase::__construct().
     *
     * @param string $collection
     *   The name of the collection holding key and value pairs.
     * @param \Drupal\Component\Serialization\SerializationInterface $serializer
     *   The serialization class to use.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection to use.
     * @param string $table
     *   The name of the SQL table to use, defaults to key_value.
     */
    public function __construct($collection, SerializationInterface $serializer, Connection $connection, $table = 'key_value') {
        parent::__construct($collection);
        $this->serializer = $serializer;
        $this->connection = $connection;
        $this->table = $table;
    }
    
    /**
     * {@inheritdoc}
     */
    public function has($key) {
        return (bool) $this->connection
            ->query('SELECT 1 FROM {' . $this->connection
            ->escapeTable($this->table) . '} WHERE collection = :collection AND name = :key', [
            ':collection' => $this->collection,
            ':key' => $key,
        ])
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMultiple(array $keys) {
        $values = [];
        try {
            $result = $this->connection
                ->query('SELECT name, value FROM {' . $this->connection
                ->escapeTable($this->table) . '} WHERE name IN ( :keys[] ) AND collection = :collection', [
                ':keys[]' => $keys,
                ':collection' => $this->collection,
            ])
                ->fetchAllAssoc('name');
            foreach ($keys as $key) {
                if (isset($result[$key])) {
                    $values[$key] = $this->serializer
                        ->decode($result[$key]->value);
                }
            }
        } catch (\Exception $e) {
            // @todo: Perhaps if the database is never going to be available,
            // key/value requests should return FALSE in order to allow exception
            // handling to occur but for now, keep it an array, always.
        }
        return $values;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getAll() {
        $result = $this->connection
            ->query('SELECT name, value FROM {' . $this->connection
            ->escapeTable($this->table) . '} WHERE collection = :collection', [
            ':collection' => $this->collection,
        ]);
        $values = [];
        foreach ($result as $item) {
            if ($item) {
                $values[$item->name] = $this->serializer
                    ->decode($item->value);
            }
        }
        return $values;
    }
    
    /**
     * {@inheritdoc}
     */
    public function set($key, $value) {
        $this->connection
            ->merge($this->table)
            ->keys([
            'name' => $key,
            'collection' => $this->collection,
        ])
            ->fields([
            'value' => $this->serializer
                ->encode($value),
        ])
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function setIfNotExists($key, $value) {
        $result = $this->connection
            ->merge($this->table)
            ->insertFields([
            'collection' => $this->collection,
            'name' => $key,
            'value' => $this->serializer
                ->encode($value),
        ])
            ->condition('collection', $this->collection)
            ->condition('name', $key)
            ->execute();
        return $result == Merge::STATUS_INSERT;
    }
    
    /**
     * {@inheritdoc}
     */
    public function rename($key, $new_key) {
        $this->connection
            ->update($this->table)
            ->fields([
            'name' => $new_key,
        ])
            ->condition('collection', $this->collection)
            ->condition('name', $key)
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteMultiple(array $keys) {
        // Delete in chunks when a large array is passed.
        while ($keys) {
            $this->connection
                ->delete($this->table)
                ->condition('name', array_splice($keys, 0, 1000), 'IN')
                ->condition('collection', $this->collection)
                ->execute();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteAll() {
        $this->connection
            ->delete($this->table)
            ->condition('collection', $this->collection)
            ->execute();
    }

}