$data Item data. * @return null|\SimplePay\Core\Model\ModelInterface */ public function add( $data ); /** * Updates a single item. * * @since 4.4.5 * * @param int $id Item ID. * @param array $data Item data. * @return null|\SimplePay\Core\Model\ModelInterface */ public function update( $id, $data ); /** * Deletes a single item. * * @since 4.4.5 * * @param int $id Item ID. * @return null|\SimplePay\Core\Model\ModelInterface */ public function delete( $id ); /** * Queries for items given a set of criteria. * * @since 4.4.5 * * @param array $args Query arguments. * @return array<\SimplePay\Core\Model\ModelInterface> List of models queried. */ public function query( $args = array() ); /** * Counts items given a set of criteria. * * @since 4.4.5 * * @param array $args Query arguments. * @return int The number of results. */ public function count( $args = array() ); }