public function __construct() {
		parent::__construct();

		// Easy Digital Downloads
		$this->schema['edd_order'] = [ $this, 'filter_by_edd_order' ];

		// WooCommerce
		$this->schema['woocommerce_order'] = [ $this, 'filter_by_woocommerce_order' ];

		// Override ET filters.
		$this->schema['purchaser_name'] = [ $this, 'filter_by_purchaser_name' ];
		$this->schema['purchaser_name__not_in'] = [ $this, 'filter_by_purchaser_name__not_in' ];
		$this->schema['purchaser_name__like'] = [ $this, 'filter_by_purchaser_name__like' ];
		$this->schema['purchaser_email'] = [ $this, 'filter_by_purchaser_email' ];
		$this->schema['purchaser_email__not_in'] = [ $this, 'filter_by_purchaser_email__not_in' ];
		$this->schema['purchaser_email__like'] = [ $this, 'filter_by_purchaser_email__like' ];
	}