General Question about Data Duplication / Normalization (Modelling)

I have the following relationships:

• Foo has_one Bar
• Bar has_many Baz
• Foo has_many Baz through Bar

Now my problem: I need to work with Foo.Baz but the information should be frozen/static.

By that I mean, whenever Bar.Baz changes, I don't want Foo.Baz to change.

In essence, Foo.Baz is some kind of log record that describes Baz at the time when Foo was created.

How do I best deal with this situation?

My first inclination is to just create another relationship between 开发者_高级运维Foo and Baz but that would add a lot of redundant data because Bar.Baz will only change very occasionally.

Is there a better way?

Could you leave it as it as and then create some scopes to get Foo.Baz based on the timestamps and not allow updates to Bar.Baz, just creates. So to get Foo.Baz, you'd get the latest

Bar.Baz when Bar.Foo == foo and Bar.baz.created_at < Foo.created_at.

I realize this isn't a great solution, but it may be a starting point...