Also update from_qu_id and to_qu_id of inverse unit conversions automatically (closes #1977)

migrations/0199.sql

@@ -0,0 +1,15 @@
+DROP TRIGGER qu_conversions_inverse_UPD;
+CREATE TRIGGER qu_conversions_inverse_UPD AFTER UPDATE ON quantity_unit_conversions
+BEGIN
+	/*
+		Update the inverse QU conversion
+	*/
+
+	UPDATE quantity_unit_conversions
+	SET factor = 1 / IFNULL(NEW.factor, 1),
+	from_qu_id = NEW.to_qu_id,
+	to_qu_id = NEW.from_qu_id
+	WHERE from_qu_id = OLD.to_qu_id
+		AND to_qu_id = OLD.from_qu_id
+		AND IFNULL(product_id, -1) = IFNULL(NEW.product_id, -1);
+END;