function setPrimary( $table, $key ) {

        $this->primary[ $table ] = $key;

        // compound keys are never auto-generated,
        // so we can assume they are required
        if ( is_array( $key ) ) {

            foreach ( $key as $k ) {

                $this->setRequired( $table, $k );

            }

        }

        return $this;

    }