Troubles with polymorphics associations

Hello,

Since some days, I try to create a dynamic user profiling system. In this system, users can use many fields defined in a list.

In these fields, there are ones which admit a scalar value (like firstname or birthday) and others which admit a collection (like skills or visited countries) of value.

I have some troubles with that… How can i manage these polymorphic fields ? Can you help me the define my models and their relations ?

Thanks for reading,

Sephi-Chan