Introducing grouped records on a portal

[SivadPT]

Hi

I have a form with a list of item to be introduced.

I can use a lookup and remember the id codes for each item, and compleat all the lines, or...

I can group several items and when I introduce the group code all the items from that group just show up on the list.

I'm using a portal to do that but the problem is that if the items file changes (ex: item 1 was from group A and now is from group B)all the records on the related file change, even the older ones. Can I freeze the data introduced on a record?

Thanks